ONLY 


forma 
nal 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


A  STUDY 


HISTOLOGICAL  CHARACTERS 


Periosteum  and  Peridental 


MEMBRANE. 

BY 

G.    V.  |  BLACK,    M.D.,  D.D.S. 

L 

PROFESSOR  OF  PATHOLOGY  IN  THE  CHICAGO  COLLEGE  OF  DKNTAL  SURGERY. 


WITH    67     ORIGINAL     ILLUSTRATIONS. 


CHICAGO: 

W .     T.     KEENER 

96  WASHINGTON  STREET. 

1887. 


COPYRIGHT, 

W.    T.    KEENER, 
1887. 


H/tl 


PREFACE. 


The  contents  of  this  volume  appeared  in  serial  form 
in  the  Dental  Review.  In  reviewing  the  matter  for 
publication  in  book  form,  I  find  that  the  subject  matter 
proper  for  a  preface  is  included  in  the  preliminary 
chapter  and  at  other  points  in  the  progress  of  the  work. 
I  have  concluded  therefore  to  let  it  remain  as  written, 
believing  that  it  will  serve  the  reader  fully  as  well,  or 
better,  than  to  bring  it  together  upon  this  page.  This 
volume  is  almost  entirely  a  record  of  my  own  personal 
observations,  written  in  the  personal  or  lecture  style. 
A  division  into  chapters  has  been  made  for  the  con- 
venience of  the  reader. 

The  volume  is  now  offered  to  the  profession  with  the 
hope  that  it  may  in  some  measure  supply  the  want  that 
has  been  felt -for  a  more  thorough  study  of  the  histolog- 
ical  characters  of  the  periosteum  and  peridental  mem- 
brane. 

G.  V.  B. 
Jacksonville,  Sept.  1,  1887. 


LIST    OF    CONTENTS. 


PREFACE 

CHAPTER  I.— Preliminary 1 

CHAPTER  II. — Tissue  elements  and  their  distribution;  Development; 
Matrix;  Cells;  Fibroblasts;  White  fibrous  tissue;  Areolar  tissue; 
Yellow  elastic  tissue;  Cellular  elements  of  the  fibrous  mem- 
branes; Cartilage  and  bone;  Relationship  of  the  connective 
tissues 6 

CHAPTER  III. — Methods  of  the  preparation  of  the  tissues 17 

CHAPTER  IV. — The  periosteum;  Histological  components  of  the 
periosteum;  Outer  layer;  Internal  layer;  Non-attached  inner 
layer,  residual  fibers,  attached  inner  layer;  Elastic  fibers,  blood 
vessels,  nerves  ....  22 

CHAPTER  V.— Cells  of  the  periosteum;  The  osteoblasts;  Functions 
of  the  osteoblasts;  Bone  corpuscles;  Osteoclasts 37 

CHAPTER  VI. — Formation  of  bone;  Subperiosteal  formation  of 
bone;  Subperiosteal  formation  of  Haversian  canals;  Lamination 
of  bone;  Removal  of  residual  fibers;  Formation  of  secondary 
Haversian  canals;  Intra-menibranous  formation  of  bone 45 

CHAPTER  VII. — Growth  of  bone  under  tendinous  attachments  and 
strong  fibrous  Burste;  Intra-cartalaginous  formation  of  bone; 
Ossification  in  the  epiphysis;  Ossification  in  the  diaphysis; 
Chondroclasts  and  the  absorption  of  cartilage;  Formation  of 
the  periosteum  beneath  the  perichondrium 55 

CHAPTER  VIII. — The  peridental  membrane;  Principal  fibers  of  the 
membrane;  Arrangement  of  the  fibers:  The  dental  ligament; 
The  gingiva;  Physical  functions  of  the  membrane 71 

CHAPTER  IX. — Interfibrous  elements  of  the  peridental  membrane; 
Blood  supply;  Sensory  function;  Nerve  supply 84 

CHAPTER  X. —  Lymphatics  of  the  peridental  membrane;  Hard 
formations  within  the  membrane 90 

CHAPTER  XI. — Osteoblasts  and  alveolar  wall;  Movements  of  the 
tooth  in  its  alveolus;  Relations  of  the  growth  of  the  alveolar 
processes  to  the  lengthening  of  the  face 96 

CHAPTER  XII. — The  cementum  and  cementoblasts;  Lamella?  of  the 
cementum;  Incremental  lines;  Growth  of  cementum  continuous; 
Fibers  of  the  cementum  102 

CHAPTER  XIII. — Irregularities  in  the  growth  of  the  cementum; 

Hypertrophies Ill 


VI  LIST   OF   CONTENTS. 

PAGE 

CHAPTER  XIV. — Absorptions  occurring  in  the  alveolus;  Absorption 
of  the  roots  of  the  temporary  teeth;  Absorption  not  dependent 
upon  the  vitality  of  the  tissue  being  absorbed;  Condition  of  the 
bone  corpuscles  during  the  progress  of  absorption;  Irregulari- 
ties of  absorption;  Absorbed  areas  in  dentine  always  repaired 
by  deposits  of  cementum;  Absorption  of  the  roots  of  permanent 
teeth;  Absorptions  of  the  alveolar  wall;  Cirvical  absorptions; 
Detachment  and  reattachment  of  the  principal  fibers  of  the 
peridental  membrane 118 


LIST  OF   ILLUSTRATIONS 


Fig.  1. — Embryonal  connective  tissues. 

Fig.  2. — The  same  a  little  more  developed. 

Fig.  3. — The  cells  developed  into  fibroblasts. 

Fig.  4. — White  fibrous  tissue. 

Fig  5. — Old  white  fibrous  tissue. 

Fig.  6. — Coarse  white  fibers  showing  mode  of  division. 

Fig.  7. — Coarse  white  fibers  breaking  up  into  fine  fibers. 

Fig.  8. — Cross  sections  of  coarse  white  fibers. 

Fig.    9. — Reticular  fibers,  showing  mode  of  division  and  the  multipolar 

cells. 

Fig.  10. — Cross  sections  of  reticular  fibers. 

Fig.  11. — Connective  tissue  cells  from  which  reticular  fibers  are  de- 
veloped. 

Fig.  12. — Network  of  elastic  fibers  from  the  point  of  reflection  of  the 
mucous  membrane  of  the  lip  from  the  gum. 

Fig.  13. — Network  of  elastic  fibers  teased  out  from  elastic  tendon. 

.Fig.  14. — Elastic  fibers  showing  their  disposition  to  curl  up  when  cut  or 
broken. 

Fig.  15. — Cross  sections  of  elastic  fibers. 

Fig.  16. — Tissue  of  the  dental  pulp. 

Fig.  17. — Non-attached  periosteum  from  the  femur  of  a  kitten. 

Fig.  18.— Periosteum  from  the  shaft  of  tibia  of  pig. 

Fig.  19. — Periosteum  from  lowei  end  of  femur  of  a  kitten, — penetrating 
fi  be  rs ,  — osteoclasts . 

Fig.  23. — Attached  periosteum  from  beneath  the  attachment  of  the  mus- 
cles of  lower  lip. 

Fig.  21. — The  more  usual  form  of  the  attached  periosteum. 

Fig.  22. — Network  of  elastic  fibers  from  the  coarse  fibrous  layer  of  peri- 
osteum. 

Fig.  23.— Bone,  with  portion  of  the  inner  layer  of  attached  periosteum 
and  penetrating  fibers. 

Fig.  24. — Bone,  showing  a  solid  subpenosteal  growth  and  the  manner  of 
forming  secondary  Haversian  systems. 

Fig.  25. — Margin  of  growing  bone  on  which  the  osteoblasts  are  very 
much  crowded. 

Fig.  26. — Cross  section  of  growing  bone  showing  the  Haversian  canals 
and  the  plan  of  their  subpenosteal  formation. 

Fig.  27. — Absorption  of  bone  under  the  attached  periosteum. 

Fig.  28. — Intra-membranous  formation  of  bone. 

Fig.  29. — Growth  of  bone  under  the  attachment  of  tendo-Achillis. 


Vlii  LIST    OF   ILLUSTRATIONS. 

Fig.  30. — Epiphytal  intra-cartalagenous  formation  of  bone.  Manner  in 
which  absorption  occurs. 

Fig.  31. — Epiphysal  intra-cartalagenous  formation  of  bone. 

Fig.  32.— Central  section  of  head  of  tibia  showing  relations  of  diaphysal 
and  epiphysal  formation  of  bone. 

Fig.  33. — Changes  which  occur  in  diaphysal  intra-cartalegenous  forma- 
tion of  bone. 

Fig.  34.— Ibid,  supplement  to  Fiir  :;:}. 

Fig.  35. — Cross  section  of  rib  of  young  kitten  showing  the  cartilage 
remaining  in  the  newly  formed  bone. 

Fig.  36.— Lengthwise  section  of  incisor  tooth  with  its  membrane  and 
alveolor  process. 

Fig.  37.— Cross  section  of  the  root  of  a  temporary  tooth  with  its  mem- 
brane and  alveolar  process. 

Fig.  38. — Cross  section  of  cuspid  tooth  (adult)  with  its  membrane  and 
alveolar  process. 

Fig.  39. — Fibers  of  peridental  membrane  passing  from  the  cementum  to 
the  alveolar  wall. 

Fig.  40. — Cross  sections  of  central  and  lateral  incisors  near  the  gingivae, 
showing  the  tissue  intervening  between  the  teeth. 

Fig.  41. — The  peridental  membrane  from  a  perpendicular  section  of  the 
tooth  and  alveolus  of  a  pig. 

Fig.  42. — Fibers  emerging  from  the  cementum  and  breaking  up  into 
fasciculi 

Fig.  43. — A  group  of  fibers  emerging  from  the  cementum  and  radiating 
fanlike. 

Fig.  45. — Portion  of  alveolar  wall,  and  portion  of  the  peridental  mem- 
brane, showing  the  osteoblasts. 

Fig.  46  — Very  large  fibers  of  peridental  membrane  with  inter-fibrous 
tissue 

Fig.  41.— Lymph  folicle,  or  node,  from  peridental  membrane. 

Fig.  48. — Lymph  ducts  crowded  with  lymphoid  cells 

Fig.  49.— Calcospherite-like  spherule  in  the  tissues  of  the  peridental 
membrane. 

Fig.  50. — Cementum  and  portion  of  peridental  membrane. 

Fig.  51.— Perpendicular  section  through  the  rim  of  the  alveolar  wall. 

Fig.  52. — Diagramatic  representation  of  the  movement  of  the  teeth  in 
their  alveoli.  Minimum  movement. 

Fig  53. — Ibid     Maximum  movement 

Fig.  54.— Cementoblasts  isolated  to  show  their  forms. 

Fig.  55.' — Cementoblasts  in  situ  with  cross  sections  of  the  principal  fibers 
of  the  peridental  membrane. 

Fig.  56. — Horizontal  section  of  cementum  showing  cross  sections  of  its 
fibers. 

Fig.  57.— Perpendicular  section  of  the  cementum  of  the  pig,  showing  its 

fibers. 
Fig.  58. — Cementum  of  pig  from  a  dried  section 

Fig.  59. — Hypertrophy  of  cementum.  Xodule  on  the  side  of  the  root  of 
a  lower  molar. 


LIST   OF   ILLUSTRATIONS.  IX 

Fig.  60. — Hypertrophy  of  cementum  from  the  side  of  the  root  of  cuspid 
tooth. 

Fig.  61. — Apex  of  root  of  upper  bicuspid  with  hypertrophy  of  cementum. 

Fig.  62. — Absorbed  area  of  root  of  temporary  tooth  partly  refilled  by 
cementum. 

Fig.  63. — Absorption  of  alveolar  wall.     Osteoclasts. 

Fig.  64 — Absorption  of  alveolar  wall. 

Fig.  65. — Partially  absorbed  root  of  lower  molar  repaired  by  deposit  of 
cementum. 

Fig.  66. — Pit-like  absorption  in  the  side  of  a  root  in  process  of  repair  by 
deposit  of  cementum. 

Fig.  67. — Apex  of  the  root  of  a  cuspid  tooth,  showing  areas  of  absorp- 
tion repaired  by  deposits  of  cementum. 


Fig.  1.  Embryonal  connective  tissue  in  an  early  stage  of  develop- 
ment, showing  the  cellular  elements  imbedded  in  the  ground  substance. 

Fig.  2.  The  same,  a  little  more  developed,  showing  the  cellular  ele- 
ments lengthening  in  a  common  direction. 

Fig.  3.  The  cells  developed  in  spindle  forms,  fibro  blasts  with  long 
filaments  extending  from  either  end. 

Fig.  4.    The  developed  white  fibrous  tissue. 

Fig.  5.  Older  white  fibrous  tissue,  in  which  the  cells  are  no  longer 
seen,  and  showing  the  wave-like  course  of  the  fibers. 

Fig.  6.  Coarse  white  fibers,  made  up  of  bundles  of  the  fine,  and 
showing  the  mode  of  division  by  the  splitting  off  of  a  portion  of  the  fibers 
of  the  bundle. 

Fig.  7.     Coarse  fiber  breaking  up  into  fine  fibers. 

Fig.  8.  Cross  sections  of  coarse  fibers  showing  some  of  their  various 
forms. 


Fig.  9.  Reticular  fibers,  showing  the  mode  of  division  and  the  multi- 
polar,  or  irregular  star  forms  of  the  cells  at  the  divisions. 

Fig.  10.  Cross  sections  of  the  reticular  fibers,  showing  some  of  their 
forms. 

Fig.  11.  Connective  tissue  cells  from  which  reticular  fibers  are 
developed. 

Fig.  12.  Network  of  elastic  fibers  from  the  point  of  reflection  of  the 
mucus  membrane  of  the  lip  from  the  gums. 

Fig.  13.  Network  of  elastic  fibers  teased  out  from  elastic  tendon, 
and  showing  the  usual  mode  of  division. 

Fig.  14.  Elastic  fibers,  showing  their  disposition  to  curl  up  when 
cut  or  broken. 

Fig.  15.  Cross  sections  of  elastic  fibers,  showing  their  forms  as  seen 
in  a  group  passing  between  coarse  white  fibers. 

Fig.  16.  Tissue  of  the  dental  pulp,  in  which  the  development  of  the 
cells  is  not  followed  by  any  considerable  formation  of  fibers. 


Fig.  17.  Non-attached  periosteum  from  the  shaft  of  the  femur  of  the 
kitten.  B.  Bone.  0.  Layer  of  osteoblasts.  In  the  central  portion  of 
the  figure  they  have  been  pulled  slightly  away  from  the  bone,  displaying 
the  processes  to  advantage.  It  will  be  observed  that  the  fibers  of  the 
periosteum  do  not  enter  the  bone.  a.  Inner  layer  of  fine  white  fibrous 
tissue  (osteogenetic  layer)  showing  the  neuclei  of  the  fibroblasts  and  a 
number  of  developing  connecting  tissue  cells,  which  probably  become 
osteoblasts.  c.  Outer  layer,  or  coarse  fibrous  layer,  in  which  fusiform 
fibroblasts  are  also  rendered  apparent  by  double  staining  with  hema- 
toxylin  and  carmine,  d.  Some  remains  of  the  reticular  tissue  connecting 
the  superimposed  tissue  with  the  periosteum. 

Fig  18.  Periosteum  from  the  shaft  of  the  tibia  of  the  .pig,  length- 
wise section,  showing  the  complex  arrangement  of  fibers  in  the  coarse, 
or  outer  fibrous  layer  that  sometimes  occurs  under  muscles  that  perform 
sliding  movements  upon  it  B.  Bone.  0  Layer  of  osteoblasts  The 
tissue  has  been  pulled  slightly  away  from  the  bone  in  mounting  the  sec- 
tion, and  part  of  the  osteoblasts  have  clung  to  the  bone,  some  have  clung 
to  the  tissues,  while  others  are  suspended  midway,  their  processes  cling- 
ing to  each.  a.  Layer  of  fine  fibers.  Inner  or  osteogenetic  layer  of  the 
periosteum,  b.  First  lamella  of  the  coarse  or  outer  fibrous  layer,  the 
fibers  of  which  are,  in  this  case,  circumferential,  exposing  the  cut  ends. 
It  will  be  observed  that  there  are  ten  lamellae  in  the  make-up  of  the  outer 
layer,  the  lengthwise  and  circumferential  fibers  alternating.  The  ones 
marked/,  and  i,  are  very  delicate  ribbon-like  forms,  which  have  shifted 
from  their  normal  position  in  the  mounting  of  the  section,  so  as  to  pre- 
sent their  sides  to  view  instead  of  their  ends,  thus  displaying  their  struc- 
ture to  advantage.  The  illustration  shows  how  readily  separable  these 
lamellie  are.  I.  Heticular  tissue. 

Fig.  19.  Periosteum  from  the  lower  end  of  the  femur  of  the  kitten 
at  a  point  where  the  enlarged  end  next  the  joint  is  being  trimmed  down 
for  the  elongation  of  the  shaft,  showing  the  fibers  of  the  periosteum  in- 
cluded in,  or  entering  the  bone,  forming  its  attachment,  the  absence  of 
osteoblasts  and  the  presence  of  osteoclasts  by  which  the  outer  portions  of 
the  bone  are  being  removed.  B.  Bone.  c.  Osteogenetic,  or  inner  layer 
of  periosteum,  d.  Outer  layer,  a  part  of  which  seems  to  have  been  torn 
away  E.  A  few  circumferential  fibers,  f.f.f.  Osteoblasts  lying  in  the 
lacunae  of  Howship,  or  excavations  in  the  bone  made  by  these  cells. 

Fig.  20.  Attached  periosteum  from  beneath  the  attachment  of  the 
muscles  of  the  lower  lip  of  the  sheep,  a.  Bone.  B.  Osteoblasts,  with 
the  fibers  emerging  from  the  bone  between  them.  c.  Inner  layer  with 
fibers  decussating  and  joining  the  inner  side  of  the  coarse  fibrous  layer 
in  opposite  directions.  This  is  rather  an  unusual  form  of  this  layer  of 
the  periosteum.  D.  Coarse,  fibrous  layer.  E.  Attachment  of  muscular 
fibers. 


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Fig.  21.  The  more  usual  form  of  the  attached  periosteum.  A.  Bone, 
showing  the  residual  fibers  (penetrating  fibers  of  Sharpey)  within  its  sub- 
stance and  passing  out  between  the  osteoblasts  B,  and  breaking  up  into 
fine  fibers,  which  form  the  internal  layer  of  the  periosteum.  These  are 
also  seen  protuding  from  the  broken  margins  of  the  section  at  g.g.g. 
D.  Blood-vessels  which  are  cut  across.  They  occur  mostly  in  the  inner 
layer,  very  close  to  the  under  side  of  the  outer  layer.  A  number  of 
them  are  seen.  H.  Small  nerve  bundles.  F.  Attachment  of  muscular 
fibers.  It  will  be  noted  that  the  Haversian  canals  at  li.1i.  h.  h.,  and  at 
other  points,  are  filling  up  with  bone  that  has  no  residual  fibers. 

Fig.  22,  Network  of  elastic  fibers  from  the  coarse  fibrous  layer  from 
a  section  of  the  same  series,  as  Fig.  21,  after  dissolving  out  the  coarse 
fibers  with  caustic  potash.  High  power. 

Fig.  28.  Bone,  with  portion  of  inner  layer  of  attached  periosteum, 
and  penetrating  fibers.  The  section  is  cut  across  the  Haversian  canals, 
and  it  shows  the  manner  of  the  formation  of  these  in  the  surface  of  the 
growing  bone  at  a.  a.  by  the  upward  growth  of  spiculse  of  bone  which 
then  spread  out  and  join  with  others,  thus  bridging  over  and  forming 
canals.  At  b.  b.  b.  b.  four  Haversian  canals  are  seen  lined  with  osteo 
blasts.  Around  each  of  these,  fresh  bone  is  being  deposited,  which  may 
be  recognized  by  a  slight  difference  in  shade,  but  especially  by  the  fact 
Unit  the  bone  corpuscles  lie  in  a  different  position  from  others  in  their 
neighborhood,  and  the  fact  that  this  bone  has  no  residual  fibers.  It 
should  be  noted  that  this  formation  of  canals  immensely  increases  the 
area  upon  which  osteoblasts  may  build. 

Fig.  24.  Bone,  with  a  more  solid  growth  of  surface,  and  with  osteo- 
blasts much  crowded  between  the  fibers  of  the  periosteum  as  ther  emerge 
from  the  bone.  Only  a  part  of  the  inner  layer  of  periosteum  is  shown. 
(t.  a.  Osteoblasts  several  layers  deep  between  the  fibers  of  the  periosteum. 
b.  b.  Spiculse  of  bone  growing  up  into  the  periosteum,  apparently  fol- 
lowing the  line  of  a  particular  fiber.  C.  A  Haversian  canal  that  seems 
to  have  been  excavated  in  the  bone,  and  is  being  filled  by  deposit  of  new 
bone  on  its  walls.  This  new  deposit  of  bone  is  distinguished  by  a  some- 
what lighter  shade,  and  the  difference  in  the  direction  of  the  long  axis  of 
the  bone  corpuscles,  and  the  absence  of  residual  fibers.  Osteoblasts  ap- 
pear in  this  portion  of  the  canal.  The  margins  of  the  secondary  forma- 
tion, show  the  bay-like  forms  usual  in  the  absorption  of  bone.  Above 
the  line  drawn  at  E,  no  secondary  bone  is  found,  and  osteoclasts,  g.  g, 
are  seen  instead  of  osteoblasts.  In  this  portion  the  excavation  is  going 
on.  In  this  way  the  bone,  with  residual  fibers,  is  removed  and  bone  de- 
posited in  which  these  do  not  appear. 


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Fig.  25,  12th  in.  immersion  obj.  Higner  eye  piece.  Margin  of 
growing  bone  upon  which  the  osteoblasts  are  very  much  crowded,  a, 
Osteoblasts  reaching  to  the  surface  of  the  bone  by  extending  process-like 
prolongations,  b,  A  cell  that  seems  to  be  flattening  down  upon  the  sur- 
face of  the  bone,  c,  Bone  corpuscles,  the  processes  of  which  are  seen 
radiating  in  the  bone  matrix.  Processes  are  also  seen  extending  into  the 
bone  from  some  of  the  osteoblasts. 

Fig.  26,  1-2  in.  obj.  Cross  section  of  a  young  growing  bone,  show- 
ing the  Haversian  canals  and  the  plan  of  their  subperiosteal  formation. 

a,  Outer  layer  of  periosteum,     b,     Inner  layer  of  periosteum,     c,  c, 
SpiculfB  of  bone  growing  outwards  into  the  tissue  of  the  inner  layer  of 
periosteum,     d,     Other  and  older  spiculse  spreading  out  at  their  sum- 
mits, forming  portions  of  arches,     e,    Other  spiculse,  the  arches  of  which 
are  about  closing  to  form  Haversian  canals.    /,     Complete  Haversian 
canals,  many  of  which  are  seen  in  the  illustration. 

Fig.  27,  1-8  in.  obj.  Absorption  of  bone  under  attached  periosteum. 
a,,  a,  Osteoclasts  lying  in  deep  excavations  in  the  surface  of  the  bone. 

b,  b,     Surface  of  bone,  showing  the  fibers  of  the  periosteum  implanted 
in  it.     Residual  fibers  appear  in  the  bone.     It  will  be  noted  that  these 
fibers  are  removed  with  the  bone  by  the  absorptive  process,    c,  e,    Masses 
of  fetal  tissue  filling  the  areas  formed  by  the  absorption. 

Fig.  28,  12th  inch  immersion  obj.  Intra-membranous  formation  of 
bone.  An  island  of  bony  deposit,  a,  a,  Bone  corpuscles,  b,  b,  Osteo- 
blasts. It  will  be  seen  that  these  lie  between  the  fibers  of  the  membrane, 
so  that  in  certain  positions  the  osteoblasts  lie  with  their  ends  to  the  form- 
ing bone.  And  for  the  most  part  the  long  axes  of  the  bone  corpuscles 
have  a  similar  direction. 


/V,-?;?/ 


. 


lli'f  if  ill 

4    1 

i| 

IN 


a 


V-  X 


, 


.-•••'i :'.'§•'. 


V7.    -^', 

v^vi); 


Fig.  29,  1-4  in.  obj.  Growth  of  bone  under  the  attachment  of  the 
Tendo  Achillis  in  a  young  lamb.  A,  Fibers  of  tendon  partially  con- 
verted into  fibro-cartilage.  The  cartilage  cells  are  seen  mostly  between 
the  tendon  fibers.  B,  B,  and  c,  c,  c,  Canals  advancing  from  the  bone 
beneath  into  the  tendon.  D,  D,  D,  Bone  deposited  upon  the  walls  of 
the  canals  forming  Haversian  systems  laid  upon,  or  among  the  tendon 
fibers.  E,  Portions  of  the  tendon  fibers  still  remaining  deep  among  the 
Haversian  systems  of  bone. 

Fig.  30,  12th  in.  immersion  obj. — reduced.  A  Single  canal  as 
shown  at  b,  fig.  31,  very  much  enlarged,  a,  a,  Cartilage,  b,  b,  Tissue 
of.  canal,  c,  Blood  vessel,  d,  d,  Bone,  e,  e,  Osteoblasts.  /,  /, 
Chondroclasts.  In  both  these  figures  the  bay-like  excaeations  of  the 
absorption  cells  are  seen  in  the  canals,  and  at  the  margins  of  the  bone  de- 
posited in  these. 

Fig.  31,  1-4  in.  obj.  Epiphysal  intra-cartilaginous  formation  of 
bone  from  head  of  tibia  of  young  lamb,  a,  a,  Cartilage,  the  cells  of 
which  have  fallen  into  rows,  but  have  become  scattered  between  the  let- 
ters a,  and  b,  b.  b,  b,  Haversian  canals  advanced  from  the  bone  into 
the  cartilage.  It  should  be  noticed  that  these  are  lined  with  chondro- 
clasts  where  the  absorption  of  cartilage  is  in  progress,  and  with  osteoblasts 
when  bone  is  being  deposited.  C,  Blood  vessels,  d,  d,  d.  Bone, 
which  is  extended  into  the  cartilage  by  the  filling  of  the  canals  formed  by 
absorption  as  shown  at  e. 


-/,.^. 


/>'  #  *TP 


^'"'  -^r 


Fig.  32.  Low  power.  Central  section  of  the  head,  and  portion  of 
the  shaft  of  the  tibia  from  young  kitten,  showing  diaphysal  iutra-cartila- 
ginous  formation  of  the  bone  at  d,  and  the  beginning  of  the  epiphysal  at 
h.  a,  Cartilaginous  head  of  bone,  b,  b,  Periosteum,  c,  c,  Layer 
of  subperiosteal  bone.  e.  Periosteal  notch  ;  the  point  to  which  the  sub- 
periosteal  formation  of  bone  extends.  /,  Beginning  of  change  in  the 
cartilage  cells  where  they  form  rows,  y,  Line  of  absorption  of  the 
cartilage.  At  d,  the  darkened  portion  reaching  up  to  the  line  g,  shows 
the  portion  occupied  by  the  bone  marrow,  and  the  light  portions  the 
bone  formed. 

Fig.  33,  1-8  in.  obj.  The  changes  which  occur  in  diaphysal  intra- 
cartilaginous  formation  of  bone,  a,  Cartilage  unchanged.  At  B,  the 
cells  have  become  smaller  and  have  fallen  into  rows.  At  (J,  the  cells 
are  enlarged  in  their  short  diameters,  or  in  the  direction  of  the  length 
of  the  shaft  of  the  bone.  At  D,  the  growth  of  the  cells  has  reached 
its  limit.  The  matrix  begins  to  calcify.  At  E,  the  capsules  of  the 
cells  are  opened  by  the  advance  of  the  absorbent  tissue.  F,  Area  of  the 
formation  of  bone.  g.  Apparently  some  glutinous  remains  of  the  cell 
body  clinging  to  the  walls  of  the  capsule,  h,  Small,  round  cells— mar- 
row cells,  p,  p,  p,  Remains  of  the  cartilage  matrix,  j,  Osteoblasts 
applied  to  the  remains  of  cartilage  matrix,  but  no  bone  is  seen.  K,  K,  K, 
Osteoblasts  and  a  layer  of  bone  deposited  on  the  remains  of  cartilage 
matxir.  m,  in,  m,  m,  Blood  vessels,  n,  Capsule  which  seems  to  have 
been  just  opened  and  the  marrow  cells  seen  in  the  act  of  crowding  into 
it.  o,  Fusiform  cells.  Many  of  these  appear  in  this  portion  of  the  fig- 
ure, and  seem  peculiar  to  this  location. 

Fig.  [34.  Supplement  to  fig.  33,  taken  from  another  portion  of  the 
section  and  showing  the  marrow  cells  applied  closely  to  the  walls  of  the 
capsules  next  to  be  opened,  a,  Cartilage.  b,  Fusiform  cells  filling 
closely  the  last  capsule  opened  in  that  row.  c.  c,  Round,  marrow  cells 
filling  other  capsules  in  the  same  manner,  d,  Unabsorbed  remains  of 
cartilage  matrix.  . 

Fig.  35,  1-8  in.  obj.  From  a  cross  section  of  a  rib  of  a  young  kitten 
at  a  little  distance  (boneward)  from  the  change  from  cartilage  to  bone, 
showing  the  large  Haversian  canals  with  the  remains  of  the  cartilage 
matrix  enveloped  in  the  bone  formed,  a,  a,  a,,  a,  Remains  of  cartilage 
matrix  which,  in  the  figures,  is  left  white,  b,  b,  b,  b,  Bone  deposited  on 
remains  of  cartilage  matrix,  and  generally  covered  with  Osteoblasts,  but 
at  c,  c,  c,  c,  and  other  points,  osteoclasts  are  quite  plentifully  distributed. 
While  in  one  part  bone  is  being  deposited,  in  another  it  is  being  removed, 
and  in  the  end  all  the  cartilage  matrix  disappears. 


Fig.  36,  2  in.  obj.  Lengthwise  section  of  small  incisor  tooth  of  kit- 
ten with  its  membrane  and  alveolus.  The  portion  included  in  the  illus- 
tration is  one-fourth  in.  long,  a,  a,  Crown  of  tooth  and  dentine,  b, 
Pulp  chamber  and  root  canal,  c,  Cementum.  d,  d,  d,  d,  Alveolar  walls. 
e,  Apical  space  and  apical  foramen.  f,f,f,f,  Body  of  perideutal  mem- 
brane, showing  particularly  the  arrangement  of  its  principal  fibers,  their 
direction,  etc.  g,  g,  The  cervical  portion  of  the  peridental  membrane, 
showing  the  relation  of  its  fibers  to  the  gingivus  7i,  the  tangled  mass  of 
fibers  forming  the  gums  k,  and  the  periosteum  n,  n,  of  the  outer  surface 
of  alveolar  wall,  h,  h,  Gingivus.  j,j,  Epithelium,  k,  k,  Coarse  fibrous 
tissue  of  the  gums.  I,  I,  I,  Bloodvessels  traversing  the  peridental  mem- 
brane. A  section  showing  the  smallest  number  of  these  was  selected,  for 
the  reason  that  the  fibrous  arrangement  is  less  distorted.  *  m,  Saculus  of 
permanent  tooth.  The  fibers  of  the  peridental  membrane  become  con- 
tinuous with  those  of  the  periosteum  at  n,  n.  o,  Periosteum,  p,  Attach- 
ment of  labial  muscles.  The  intention  of  the  illustration  is  to  give  a  full 
view  of  the  arrangement  of  the  fibers  of  the  peridental  membrane,  and 
the  relations  of  the  tooth,  membrane,  and  alveolar  wall. 


Fig.  37,  2  in.  obj.  Cross  section  of  the  root  of  a  temporary  incisor 
with  the  peridental  membrane  and  alveolar  walls,  at  about  the  middle  of 
the  lower  third  of  body  of  the  peridental  membrane,  showing  the 
direction  of  the  fibers  of  the  membrane,  and  the  position  of  the  blood-ves- 
sels, a,  The  dentine,  b,  Cementum.  c,  Pulp.  Its  blood-vessels  are  shown. 
d,  d,  Alveolar  wall,  septi  between  the  teeth,  e,  e,  Peridental  membrane. 
The  direction  and  arrangement  of  its  fibers  have  been  carefully  repre- 
sented; also  the  position  and  relative  size  of  its  blood-vessels.  /,  Thin 
portion  of  the  anterior  alveolar  wall,  g,  Hypertrophy  of  the  cernentum. 

Fig.  38,  2  in.  obj.  Cross  section  of  cuspid  tooth  with  peridental 
membrane  and  alveolar  wall  cut  through  the  thickened  rim  at  the  gin- 
gival  portion  of  the  alveolar  wall,  from  a  man  forty  years  old.  The 
membrane  was  very  thin  and  firm,  and  a  large  piece  of  the  anterior  wall 
of  the  alveolus  adhered  to  the  tooth  when  extracted.  It  therefore  repre- 
sents an  extremely  thin  membrane,  while  fig.  37  represents  one  that  may 
be  regarded  as  thick,  a,  a,  Peridental  membrane,  b,  b,  Cementum.  c, 
c,  Alveolar  process,  d,  d,  Dentine.  It  will  be  observed  that  most  of  the 
blood-vessels  of  the  peridental  membrane  lie  in  depressions  in  the  alveolar 
wall. 

Fig.  39,  |  in.  obj.  Fibers  of  the  peridental  membrane  passing  from 
the  cementum  a,  to  the  alveolar  wall  b.  The  section  is  from  the  root  of 
a  first  molar  of  a  man  about  seventy  years  old.  The  point  chosen  for 
this  illustration  includes  a  portion  of  a  strong  band  of  solid  fibers  c, 
which  pass  unbroken  from  the  cementum  to  the  bone.  More  generally, 
the  fibers,  after  emerging  from  the  cementum,  break  up  into  finer  fibers 
or  fasciculi,  as  at  d.  This  form  of  the  fibers  is  better  shown  in  fig.  42. 


Fig.  40,  2.  in  obj.  Cross  section  of  the  central  and  lateral  incisors 
bdow  (toward  the  crowns)  the  rim  of  the  alveolar  wall,  or  through  the 
necks  of  the  teeth,  showing  the  tissue  of  the  septum  and  of  the  gums 
anteriority,  a,  Portion  of  central  incisor,  b,  Lateral  incisor,  e,  Pulp 
chamber  of  lateral  incisor,  d,  d,  Cementum  of  central  incisor,  e,  e,  Ce- 
mentum  of  lateral.  /,  Fibers  of  the  peridental  membrane  extending 
from  tooth  to  tooth  continuously.  These  are  fixed  in  the  cementum  of 
each  tooth,  and  form  the  tissue  of  the  septum,  g,  g,  Fibers  of  the  peri- 
dental  membrane,  which  join  with  the  coarse  fibrous  tissues  of  the  gums 
//,  }>.  ./',,/,  Epithelial  covering  of  the  gums. 

Fig.  41,  £  in.  obj.  Peridental  membrane  from  perpendicular  section 
of  a  tooth  of  the  pig,  stained  with  nucleus  tinting  dye.  a,  Cementum. 
b,  Bone,  e,  Blood-vessels  cut  diagonally,  d,  Nerve  bundle,  e,  Lym- 
phatics. A  number  of  these  are  seen  near  the  cementum.  The  principal 
fibers  are  transparent,  while  the  interfibrous  tissue  is  stained.  The  cellu- 
lar elements  appear  in  rows  between  the  principal  fibers,  which  are  large 
and  strong  near  the  bone,  and  only  partially  break  up  into  fasciculi  in  the 
central  part  of  their  length. 

Fig.  42, 12th  in.  obj.  (reduced.)  Fibers  emerging  from  the  cementum 
and  breaking  up  into  fasciculi.  From  the  peridental  membrane  of  a 
molar  of  an  aged  person.  This  represents  the  more  usual  form  of  the 
principal  fibers,  as  seen  in  old  age  in  man.  They  pursue  a  somewhat 
wavy  course,  and  generally  the  identity  of  the  individual  fiber  is  lost. 
They  are  inserted  into  the  bone  in  compact  bundles  similar  to  those  of 
the  cementum. 

Fig.  43,  12th  in.  obj.  (reduced.)  A  group  of  fibers  emerging  from 
the  cementum  and  radiating  fan-like.  On  either  side,  the  principal 
fibers  are  absent  for  a  little  space,  which  is  filled  with  indifferent  tissue. 
From  the  apical  space  (at  the  apex  of  the  root)  of  a  bicuspid  of  an  old 
person. 


a- 


&-•'/.  -  " '•'•• ;  ''''•• 
• 


'y/ 


Fig.  45,  12th  in.  obj.  (reduced.)  From  section  including  a  portion 
of  the  alveolar  wall,  and  portions  of  the  peridental  membrane,  showing 
tin-  osteobla-<ts.  a,  Bone.  Inner  margin  of  alveolar  wall,  showing resdi 
ual  fibers,  b,  Osteohlasts.  Developing  cells  are  seen  in  the  neighbor- 
hood, e,  Fibers  of  the  peridental  membrane.  It  will  be  noted  that  these 
spring  from  the  bone  as  solid  fibers  and  immediately  break  up  into 
fasciculi. 

Fig.  46,  12th  in.  obj.  (reduced.)  From  section  including  a  portion 
of  the  alveolar  wall,  and  fibers  of  the  peridental  membrane  at  a  point 
where  these  latter  are  large  and  compact,  and  with  interfibrous  tissue 
between  them,  a,  Bone,  showing  the  large  residual  fibers,  b,  Osteo- 
blasts  filling  spaces  between  the  fibers,  c,  Principal  fibers  of  peridental 
membrane,  which  at  this  point  maintain  the  solid  form  far  out  from  the 
bone,  d,  Interfibrous  tissue  consisting  of  fibroblasts  and  fibers  which  lie 
between  the  principal  fibers  and  pursue  an  independent  course.  Compare 
with  fig  I."). 

Fig.  47,  12th  in.  obj.  (reduced.)  A  lymph  follicle  or  node  from 
near  the  gingival  border  of  the  peridental  membrane,  a,  a,  a,  Lymph- 
cells  seemingly  inclosed  within  enlarged  lymph-ducts,  b,  b,  Capillary 
vessel. 

Fig.  48,  J  in.  obj.  Lymp-ducts  crowded  with  lymphoid  cells. 
From  a  section  taken  horizontal  to  the  surface  of  the  cementum,  but  a 
very  slight  distance  from  it.  Cross  cuts  of  these  are  seen  at  c,  c,  jn  fig.  50. 

Fig.  49,  i  in.  obj.  Calcospherite-like  spherule  in  the  tissues  of  the 
peridental  membrane,  a,  Spherule,  b,  Cementum,  showing  the  fibers 
of  the  peridental  membrane  springing  from  it.  c.  Principal  fibers  of 
membrane,  d,  Indifferent  tissue.  For  a  small  space  no  fibers  are  at- 
tached to  the  cementum. 


In 

Wm 


\  \U>  fttS^  rlf/ 

H 

v-   N  '  *i*  y  *\ 

S/%    ^    ?  %'  -    •          -',"•       '       '       «     --":       *•       "«> 

•    ^        ------ 


Fig.  50,  12th  in.  obj.  (reduced.)  Cementum  and  portion  of  the  peri- 
dental  membrane  from  the  sheep.  From  a  cross  section  of  the  tooth. 
a,  Cementum.  B,  Cementoblast  lying  between  the  fibers,  which  latter 
break  up  into  fasciculi  immediately  after  leaving  the  cementun.  c,  c, 
Cross  section  of  the  lymph  follicles  or  nodes.  D,  Fibroblasts.  E,  Blood 
vessels.  These  are  accompanied  by  a  large  amount  of  interfibrous,  or 
indifferent  connective  tissue.  F,  Nerve  bundle.  G-,  Fasciculi  of  fibers 
pursuing  a  direction  different  from  the  main  trend  of  the  principal 
fibers. 

Fig.  51,  |  in.  obj.  Rim  of  the  alveolar  wall,  from  a  perpendicular 
section,  a,  Haversian  bone,  which  is  left  without  stippling  to  render  it 
more  apparent,  b,  Subperiosteal  bone,  showing  residual  fibers,  c,  Per- 
iosteum, d,  Extreme  gingival  margin  of  the  alveolar  wall,  e,  Fibers  of 
tbe  peridental  membrane.  /,  Bone  formed  by  the  osteoblasts  of  the  peri- 
dental  membrane,  g,  g,  g,  Points  at  which  the  absorption  of  bone  is  in 
progress. 

Figs.  52  and  53.  Diagramatic  illustration  of  the  movement  of  a 
central  incisor  during  the  growth  of  the  alveolar  process  between  the  age 
of  twelve  aud  twenty-one  years.  The  broken  lines  represent  the  tooth 
and  its  alveolus  at  twelve  years  of  age,  and  the  solid  the  same  tooth  at 
twenty-one. 

Fig.  52  represents  the  minimum  movement,  while  fig.  53  represents 
the  maximum  movement,  as  ordinarily  observed.  The  figures  are  let- 
tered alike.  The  growth  of  the  process  is  represented  by  the  movement 
from  a,  a  to  b,  b.  The  tooth  is  carried  forward  with  this  growth,  and 
the  alveolus  is  tilled  with  new  bone  from  the  line  c,  to  the  line/. 


a 

'••  f 


« 


^ 


lit 


-:--  -c    • 


Fig.  54,  12th  in.  obj.  Cementoblasts  isolated  to  show  the  peculiar 
irregular  forms  of  these  cells. 

Fig.  55,  12th  in.  obj.  Cementoblasts  in  situ,  with  cross  sections 
of  the  principal  fibers  of  the  peridental  membrane  of  the  pig,  from  a 
section  cut  horizontal  to  the  surface  of  the  cementum  and  including 
these  cells.  1 1  will  be  seen  that  the  Cementoblasts  fill  all  the  space  not 
occupied  by  the  principal  fibers.  (In  figure  57  e,  the  Cementoblasts  are 
seen  as  they  appear  in  section  perpendicular  to  the  surface  of  the 
cementuni.) 

Fig.  56,  12th  in.  obj.  Section  of  cementum  of  pig  cut  horizontal  to 
and  near  the  surface  of  the  root  of  the  tooth,  showing  cross  sections  of 
the  included  fibers,  b.  Thin  margin  of  section,  from  which  the  fibers 
have  fallen  out  of  their  alveoli,  c,  A  little  thicker  portion  in  which  the 
fibers  remain.  It  will  be  noticed  that  from  shrinkage  the  fiber  is  a  little 
small  for  its  alveolus,  so  that  it  is  slightly  separated  from  one  side,  a, 
Cement  corpuscles 

Fig.  57,  i  in.  obj.  Perpendicular  section  of  the  cementum  of  a  pig, 
showing  the  included  fibers  of  the  peridental  membrane,  e,  Margin  of 
cementum  showing  fibers  passing  from  the  cementum  to  the  peridental 
membrane,  and  the  layer  of  Cementoblasts  with  other  cells  in  the  neigh- 
borhood. /,  Lymphatics,  d,  d,  Fibers  protruding  from  broken  margin 
of  section,  a,  Dentine,  b,  Junction  of  dentine  and  cementum. 

Fig.  58,  12th  in.  obj.  Cementum  of  pig  from  the  dried  section,  a, 
Dentine,  b,  Lacunae  of  cementum  with  canals  anastomosing  with  each 
other,  c,  Imperfectly  calcified  fibers.  It  will  be  noticed  that  a  few  of 
the  dentinal  tubes  pass  through  into  the  cementum. 


r?  i 


iifpwwptw) 


Fig.  59,  1  in.  obj.  Hypertrophy  of  the  cementum  on  the  side  of  the 
root  of  a  lower  molar  near  the  neck  of  the  tooth.  From  a  lengthwise 
section,  man.  a,  Dentine,  b,  Cementum.  c,  Fibers  of  peridental  mem- 
brane. From  b  to  c  the  cementum  is  normal,  and  the  incremental  lines 
fairly  regular,  but  at  d,  one  of  the  lamclUe  is  greatly,  thickened.  At  e,. 
this  lamella  is  seen  to  be  about  equal  in  thickness  with  the  others. 

The  next  two  lamella:  are  thin  over  the  greatest  prominence,  but  one 
is  much  thickened  at  g,  and  both  at  h.  These  latter  seem  to  partially  fill 
the  valleys  which  were  occasioned  by  the  first  irregular  growth. 

Fig.  60.  1.  in  obj.  Hypertrophy  from  root  of  cuspid,  man,  in  which 
the  irregularity  is  confined  to  the  first  lamella,  a,  Dentine,  b,  Thick- 
ened first  lamella,  c,  Subsequent  lamella),  which  are  seen  to  be  fa'rly 
regular. 

Fig.  61,  2  in.  obj.  Apex  of  root  of  an  upper  bicuspid  tooth  with  ir- 
regularly developed  cementum.  a,  a,  Dentine,  b,  b,  Pulp  canals.  The 
lamelke  of  cementum  are  marked  1,  2,  3,  etc.  d,  d,  d,  Absorption  areas 
that  have  been  refilled  with  cementum. 

It  will  be  seen  that  the  apices  of  the  roots  were  originally  separate, 
but  became  fused  with  the  deposit  of  the  second  lamella  of  cementum, 
and  that  in  this  the  irregular  growth  began  and  was  most  pronounced. 
It  has  continued  through  the  subsequent  lamellae,  but  in  less  degree.  It 
will  also  be  noticed  that  the  absorption  areas,  d,  d,  d,  have  proceeded 
from  certain  lamella1.  That  between  the  roots  has  broken  through  the 
first  lamella  and  penetrated  the  dentine,  and  has  been  filled  with  the  de- 
posit of  a  second  lamella.  Other  of  the  absorptions  have  proceeded 
from  lamella.1,  which  can  be  readily  made  out.  The  small  points,  e,  seem 
to  have  been  filled  with  the  deposit  of  the  last  layer  of  the  cemeutum, 
while  others  have  one,  two  or  more  layers  covering  them. 


mam  i       L,       '• 


-~  2*  -y      y 


Fig.  62,  i  in.  obj.  Cross  section  of  the  root  of  a  temporary  incisor 
tooth  of  the  pig,  showing  a  large  area  of  absorption  which  is  partly  filled 
in  with  cenientum. 

a,  Dentine,  b,  b,  Cementum.  c,  c,  Area  of  absorption.  It  will  be 
noticed  that  in  this  area  all  of  the  cementum  and  a  considerable  portion 
of  the  dentine  has  been  removed,  d,  d,  Cementum  that  has  been  laid 
down  upon  the  surface  of  the  dentine  and  cementum  alike,  e,  e,  Peri- 
dental  membrane.  /,  Portion  of  bone  forming  the  wall  of  the  alveolus 
that  has  grown  forward  into  the  area  of  absorption,  g,  g,  Osteoclasts 
which  are  removing  these  bony  projections.  The  bone  which  has  been 
advanced  here  to  take  the  place  of  the  absorbed  area  is  being  removed 
again  in  compliance  with  the  rebuilding  of  the  cementum,  which  is  in 
progress. 

Fig.  63,  £  in.  obj.  Portion  of  the  anterior  alveolar  wall  of  an  incisor 
that  is  being  absorbed,  a,  a,  Portion  of  the  inner  layer  of  the  per- 
iosteum, b,  b,  Bone  forming  a  portion  of  the  anterior  wall  of  the  alveo- 
lus. It  will  be  observed  that  it  contains  a  number  of  Haversian  canals, 
h,  li.  c,  c,  A  portion  of  the  peridental  membrane,  d,  d,  d,  Osteoclasts 
which  are  in  the  act  of  removing  the  bone,  thus  widening  the  al- 
veolus, e,  Space  from  which  a  large  osteoclast  has  probably  fallen  dur- 
ing the  preparations  of  the  section.  It  will  be  noticed  that  where  the 
Osteoclasts  are  removing  the  bone,  the  fibers  of  the  peridental  membrane 
are  detached  and  some  little  space  is  occupied  by  tissue  of  a  fetal  type, 
but  in  the  spaces  between  the  groups  of  Osteoclasts  the  fibers  are 
firmly  attached  to  the  bone.  At  /,  there  seems  to  be  a  little  new  bone 
formed  to  which  fibers  are  attached.  In  this  way  bone  seems  to  be  re- 
moved, part  by  part,  and  the  attachment  of  the  membrane  maintained. 

Fig.  64,  |  in.  obj.  Portion  of  the  alveolar  wall  of  a  cuspid  tooth  of 
an  old  person,  showing  absorptions  a,  a,  Portion  of  the  peridental 
membrane,  b,  b,  Portion  of  bone  that  seems  to  have  been  built  on  to 
supply  an  area  of  previous  absorption,  e,  A  recent  absorption  area.  At 
/,  three  Osteoclasts  are  seen.  It  will  be  noted  that  the  fibers  of  the  peri 
dental  membrane  are  detached  throughout  this  area  of  absorption  and 
the  space  is  occupied  by  tissue  of  a  fetal  type.  It  should  also  be  noted 
that  the  Haversian  systems  of  the  bone  had  been  cut  into  by  the  previous 
absorption,  removing  portions  of  the  rings  of  the  Haversian  systems. 
Residual  fibers  are  seen  in  the  bone  b,  but  there  are  none  in  the  Haver- 
sian bone  c. 


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Fig.  65,  £  in.  obj,  One  half  of  the  apex  of  the  root  of  a  lower 
molar.  From  a  dry  section,  a.  Pulp  canal,  b,  Dentine,  c,  Cemenlum. 
A  number  of  absorptions  have  occurred  at  d.  Absorptions  have  pro- 
ceeded from  the  second  lamella  of  the  cementum  and  have  penetrated  the 
dentine  to  a  considerable  depth.  These  have  been  refilled  with  a  some- 
what irregular  deposit  of  cementum.  Along  the  line  e,  a  very  consider- 
ble  absorption  has  cut  away  the  entire  apex  of  the  root,  removing  not 
only  the  cementum,  but  evidently  a  considerable  portion  of  the  dentine 
as  well.  From  the  appearance  of  the  incremental  lines,  this  seems  to 
have  occurred  contemporaneously  with  those  pointed  out  at  d.  The  ex- 
posed dentine  has  been  again  covered  with  cementum,  which  is  fairly 
regular,  though  its  incremental  lines  are  not  clear.  /,  An  absorption 
that  seems  to  have  been  in  progress  at  the  time  of  extraction. 

Fig.  66,  i  in.  obj.  From  a  section  of  a  bicuspid  with  its  alveolus, 
showing  a  pit-like  absorption  upon  the  side  of  the  root  in  which  the  re- 
deposit  of  the  cemeutuni  has  begun,  a,  Dentine,  b,  Cemeutum.  c,  Per- 
idental  membrane,  d,  Bone  forming  the  wall  of  the  alveolus,  e,  Ab- 
sorbed area  of  cementum.  It  will  be  noticed  that  a  new  deposit  of  ce- 
mentum has  begun  the  filling  of  the  area,  and  that  the  soft  tissue  in  the 
area  of  absorption  is  of  a  cellular  type.  The  bone  also  shows  the  effects 
of  absorption  in  the  cutting  away  of  portions  of  the  rings  of  the  Haver- 
sian  systems  at  /,  while  at  g  the  presence  of  osteoclasts  shows  that  ab- 
sorption is  in  progress  at  that  point. 

Fig.  67,  •&  in.  obj.  Cross  section  of  the  immediate  apex  of  the  root 
of  a  cuspid  tooth,  showing  large  areas  of  absorption,  a,  Root  canal,  b, 
e,  ff,  and  j  show  extensive  absorption  areas  that  have  been  refilled  with 
cementum,  while  c,  d,  Ji,  and  k  show  smaller  absorption  areas  that  have 
occurred  later.  Some  of  these  areas  show  the  included  fibers  of  the  per- 
idental  membrane  plainly,  while  others  do  not,  probably  for  the  reason 
that  the  section  is  not  parallel  with  them.  At  /,  the  original  or  regular 
deposit  of  cementum  reaches  the  present  surface.  The  plane  of  the 
section  is  not  such  as  to  show  the  incremental  lines,  and  therefore  the 
relation  of  the  absorptions  to  these  cannot  be  seen. 


THE  PERIOSTEUM  AND   PERIDENTAL 
MEMBRANE. 


CHAPTER  I. 

PRELIMINARY. 

In  the  study  of  histology  there  have  been  great  ad- 
vances within  the  last  few  decades.  This  advance  has 
been  along  special  lines  to  which  attention  has  been 
strongly  drawn  by  the  results  of  individual  effort,  or  in 
which  the  needs  of  the  suffering  public  have  directed  in- 
vestigation. Cohnheim  and  Strieker,  with  numerous  co- 
laborers,  have  done  much  to  unravel  and  make  plain  the 
formerly  mysterious  tissue  changes  which  occur  in  in- 
flammation. By  the  investigations  of  numerous  workers 
the  tissue  forms  and  modes  of  growth  of  the  various 
tumors  have  been  made  so  clear,  that  even  the  young 
worker  in  pathological  anatomy  may  readily  recognize 
their  various  forms,  and  classify  properly  those  that  may 
come  under  his  lens. 

The  more  difficult  special  tissue  forms  of  the  eye  and 
ear  have  been  so  plainly  unfolded  by  workers  in  these 
fields  that  it  is  no  longer  a  question  as  to  the  forms  of 
the  elements  found,  but  the  discussion  is  carried  to  the 
domain  of  the  more  intimate  and  special  physiological 
function  of  individual  groups  of  cells  which  are  recog- 
nized by  all.  The  very  complex  structures  of  the  brain, 
spinal  cord,  and  the  various  ganglia  of  the  nervous  sys- 
tem have  been  searched  so  closely  that  the  discovery  of 
form  elements  yet  undescribed  seems  almost  impossible. 
And  as  it  is  with  these,  so  it  is  with  a  large  majority  of 

1 


2  PRELIMINARY. 

the  form  elements  of  the  human  body.  Yet  there  are 
many  special  fields  opening  up  for  further  discovery  and 
waiting  for  laborers. 

In  this  work  each  advance  in  discovery  has  brought 
with  it  a  corresponding  advance  in  technique.  New  and 
better  means  of  bringing  difficult  and  hidden  form  ele- 
ments into  view  have  been  so  rapidly  brought  forward 
that  one  who  has  been  out  of  the  work  for  but  a  few 
years  will,  on  entering  the  histological  laboratory  of  to- 
day, find  himself  confronted  by  apparatus  and  re-agents, 
much  of  which  will  seem  new  and  strange  ;  and  will  find 
that  these  have  modified  the  views  of  tissue  elements 
with  which  he  had  been  familiar,  and  have  brought  them 
into  bolder  relief,  developing  finer  elements  of  structure 
than  had  been  possible  by  the  older  methods  of  pro- 
cedure. That  which  had  been  known  becomes  better 
and  more  intimately  known  ;  and  this  better  technique 
calls  for  re-working  in  the  formerly  worked  out  mines  of 
histological  inquiry  for  the  finding  of  the  finer  grains  of 
information  missed  by  former  laborers. 

Each  field  in  histology  seems  to  be  worked  over  and 
pondered  over  anew,  as  new  pathological  factors  have 
fastened  the  attention  of  specialist  or  general  practi- 
tioner. This  is  the  case  whether  the  new  factor  be 
based  upon  some  new  fact  discovered,  or  theory  pro- 
pounded ;  for  each  thought  that  gives  promise  of  devel- 
oping truth  must  be  tried  and  tallied  with  the  form 
elements  with  which  it  is  associated. 

It  is  considerations  such  as  these  that  have  prompted 
me  to  undertake  anew  the  study  of  the  periosteum  and 
peridental  membrane.  Fifteen  years  ago  I  went  over 
the  subjects  pretty  closely,  but  at  that  time  there  seemed 
to  be  no  special  call  for  more  definite  information  in 
regard  to  them.  Upon  the  peridental  membrane  there 
had  not  been  much  written,  and  there  did  not  seem  to  be 
much  interest  in  the  subject  among  the  dental  specialists. 


PRELIMINARY.  3 

Since  then,  however,  attention  has  been  strongly  called 
to  the  structure  of  this  membrane  from  several  directions 
almost  simultaneously,  and  an  intense  interest  awakened. 
These  are,  first,  the  efforts  that  have  been  expended  in 
the  study  of  its  destructive  diseases,  which  was  stimu- 
lated primarily  by  the  late  Dr.  Riggs  of  Hartford  ;  sec- 
ondly, by  the  greater  and  more  general  interest  recently 
felt  in  the  correction  of  irregularities  of  the  teeth,  in 
which  changes  in  this  membrane  and  the  relations  of  the 
parts  which  it  unites  are  brought  about ;  third,  by  the 
greater  interest  that  has  been  manifested  by  the  masses 
of  the  dental  profession  in  the  retention  of  pulpless  teeth, 
and  roots  which  have  lost  their  crowns,  and  which  are 
dependent  upon  the  continued  health  of  the  peridental 
membrane  under  modified  conditions ;  fourth,  by  the  re- 
vival under  varied  forms  of  the  ancient  methods  of 
replanting  and  transplanting  teeth,  the  success  of  which 
is  supposed  to  be  dependent,  in  whole  or  in  part,  upon 
the  reconstruction  of  the  peridental  membrane,  or  its  re- 
attachment  to  the  teeth;  and,  fifth,  by  the  singular  fact 
that  has  of  late  been  noted  more  accurately  ;  that  a  large 
proportion  of  the  teeth  thus  replanted  with  seeming  suc- 
cess, are  finally  lost  by  absorption  of  their  roots  ;  a  matter 
which  seems  to  depend  upon  some  mal-condition  of  the 
tissues  of  the  peridental  membrane. 

All  of  these  considerations  call  earnestly  for  an  intim- 
ate knowledge  of  the  histology  and  physiology  of  this 
membrane  as  the  basis  for  the  formation  of  correct  views 
of  its  pathology  and  recuperative  powers  when  subjected 
to  disease  or  serious  injury.  In  order  that  I  might  obtain 
correct  views  for  presentation,  I  have  gone  back  to  the 
tissues  themselves  for  information  and  have  made  a  re- 
study  of  the  subject  de  novo,  availing  myself  of  the  new 
methods  of  procedure,  and  preparing  such  a  number  of 
sections  from  various  sources  as  would  seem  to  give 
every  possible  view  of  the  subject.  In  this  study  it  has 


4  PRELIMINARY. 

not  seemed  judicious  to  confine  my  labors  to  the  peri- 
dental  membrane,  either  in  the  study  or  in  the  presenta- 
tion, but  to  unite  with  it  the  study  of  the  periosteum  for 
the  purpose  of  having  a  broader  field  of  comparison. 
This  is  at  once  suggested  by  the  natural  kinship  of  these 
tissues,  and  has  been  rendered  the  more  necessary  by 
previous  views  that  have  been  entertained  as  to  the  dis- 
tinctions between  them,  or  their  identity.  Indeed,  the 
relations  of  these  membranes  are  such  that  the  perios- 
teum must  be  studied  in  order  to  arrive  at  correct  views 
in  regard  to  the  structure  and  function  of  the  peridental 
membrane,  which  will  clearly  appear  as  we  proceed. 
They  are  alike  in  many  of  their  features  while  presenting 
points  of  sharp  dissimilarity,  and  by  studying  them  to- 
gether each  becomes  better  understood.  The  task  is  an 
unusually  difficult  one  for  several  reasons.  First,  it  is 
impossible  to  obtain  suitable  sections  for  the  examination 
of  these  tissues  without  first  decalcifying  the  bones  and 
teeth  ;  for  we  must  study  them  in  their  normal  relations 
to  the  parts  with  which  they  are  associated.  The  acids 
to  which  they  must  be  subjected  in  the  process  of  decal- 
cification  are  not  without  effect  upon  the  tissues.  This 
is  injurious  in  a  large  degree,  and  robs  them  of  that 
freshness  so  necessary  to  the  gaining  of  good  views  of 
their  constituents. 

Again,  the  selective  stainings  that  are  so  valuable  in 
histological  determinations  depend  upon  the  finer  chemi- 
cal qualities  of  certain  constituents  of  the  tissues,  their 
cells,  or  fibers,  which  cause  certain  of  these  to  absorb  a 
dye  or  color  while  others  do  not,  thus  distinguishing 
them..  The  necessary  subjection  to  acids  in  decalcifica- 
tion  disturbs  these  finer  chemical  relations  seriously,  so 
seriously  as  to  render  the  use  of  some  of  the  finer  stain- 
ing agents  unavailing,  and  causing  much  annoyance  and 
imperfection  in  the  use  of  others. 

Again,  in   the  study  of  most  of  the  tissues  a  little 


PRELIMINARY.  ,  5 

•shrinkage  in  the  process  of  hardening  for  the  purpose  of 
making  sections  is  of  little  or  no  consequence,  for  all 
being  soft  they  will  presumably  shrink  in  the  same  degree, 
and  their  relations  will  not  be  disturbed;  but  in  the  mem- 
branes we  are  to  study  we  have  soft  tissues  combined  with 
bone,  and  teeth  and  their  mutual  relations  must  be  main- 
tained. If  shrinkage  occurs  in  the  softer  portions  these 
relations  are  disturbed  and  the  object  defeated. 


CHAPTER   II. 

TISSUE   ELEMENTS   AND  DISTRIBUTION. 

Before  proceeding  with  this  study  it  will  be  well  to- 
review  the  more  elementary  histology  of  the  class  of  tis- 
sues to  which  these  membranes  belong ;  to  lirst  learn  of 
what  tissue  elements  they  are  mostly  composed,  and  the 
character  of  these  elements  individually ;  and  afterward 
we  shall  be  enabled  to  study  them  more  intelligently  in 
their  combinations  and  peculiar  forms  in  special  localities. 

These  membranes  belong  to  what  is  termed  the  con- 
nective tissue  group,  and  in  structure  are  very  nearly 
related  to  many  other  parts;  so  much  so,  indeed,  that  in 
most  of  the  works  on  histology  a  description  of  the  group 
as  a  whole  has  been  considered  sufficient  without  separ- 
ate descriptions  of  the  special  membranes,  or  with  a  sim- 
ple mention  of  some  of  the  more  important  structural 
peculiarities.  This  would  seem  to  be  sufficient  to  the 
ordinary  student  of  histology  who  often  has  the  structures 
under  observation,  but  it  seems  that  to  those  who  depend 
mostly  on  reading  for  their  information  in  regard  to  such 
subjects,  which  up  to  the  present  time  includes  the  greater 
number  of  both  medical  and  dental  practitioners,  this 
does  not  serve  the  purpose  when  attention  has  been 
strongly  called  to  a  particular  one  of  these.  If  one 
attempts  to  look  up  the  special  subject  of  the  periosteum 
or  peridental  membrane  in  any  or  all  of  the  current  his- 
tological  works,  he  will  find  the  descriptions  short  and 
rather  vague  ;  indeed  that  the  literature  of  the  subject  is- 
very  incomplete.  Yet  if  these  descriptions,  short  as  they 
are,  be  taken  together  with  a  good  practical  knowledge 
of  the  histological  characters  of  the  elements  of  the  group- 


TISSUE  ELEMENTS   AND   DISTRIBUTION.  7 

of  structures  to  which  they  belong,  a  comprehensive  idea 
of  them  will  be  gained.  Still  it  must  be  admitted  that 
more  especial  description  is  needed  in  the  light  of  the 
recent  interest  awakened  in  the  peridental  membrane. 
Furthermore,  additional  studies  of  the  periosteum,  especial- 
ly from  the  pathological  standpoint,  are  very  much  needed, 
and  these  should  be  preceded  by  further  studies  of  its 
regional  histological  characters,  especially  differences  in 
the  internal  layer  and  the  varying  modes  of  its  attach- 
ment to  the  bone.  Previous  studies  of  the  periosteum 
have  related  almost  solely  to  its  bone-forming  powers 
giving  little  or  no  consideration  to  the  special  elements 
which  serve  purely  physical  functions  or  distinctions  be- 
tween these. 

This  large  group  of  fibrous  membranes  is  usually  made 
to  include  structures  which,  though  seemingly  widely 
separated,  are  closely  connected  in  their  structural  pecu- 
liarities. That  is  to  say,  though  they  may  seem  to  serve 
widely  different  purposes,  or,  better,  are  connected  with 
widely  different  organs,  they  are  all  emphatically  fibrous 
in  their  structure  and  differ  only  in  the  peculiarities  of 
their  fibrous  arrangement,  in  preponderance  of  the  white 
or  elastic  varieties,  and  in  the  number  and  character  of 
the  cells  which  may  be  contained  within  the  fibrous  net- 
work. Again  the  purposes  subserved  by  these  different 
fibrous  membranes  when  closely  studied,  are  found  to  be 
as  similar  as  their  structure.  They  are  all  coverings  for 
other  structures,  and  form  their  connections  with  neigh- 
boring parts,  and,  while  in  themselves  they  are  indifferent 
tissue,  they  are  generally  made  subservient  to  functioning 
tissues  by  conveying  bloodvessels  and  nerves,  and  holding 
in  some  part  of  their  netword  embryonal  cells  for  the 
supply  of  the  needs  of  the  tissues  which  they  envelop  or 
connect. 

DEVELOPMENT. 

The  connective  tissues  are  developed  in  a  soft  trans- 
parent homogeneous  material  which  has  been  known  as 


8  TISSUE   ELEMENTS   AND   DISTRIBUTION. 

ground  substance,  basis  substance,  gelatinous  substance  or 
matrix.  This  material  is  in  large  proportion  in  the  prim- 
itive or  developmental  state  of  this  tissue,  both  in  the 
fetus  and  in  the  early  development  of  it  as  it  occurs  in  the 
healing  of  wounds  in  the  adult.  Within  this  matrix  the 
cells  lie  imbedded,  and  in  this  state  it  is  usually  termed 
gelatinous  tissue.  In  this  matrix  the  cells  may  exist  in 
such  great  numbers  as  to  obscure  the  ground  substance, 
or  they  may  be  but  sparsely  distributed,  and  their  devel- 
opment may  be  studied  step  by  step  as  the  adult  tissues 
are  assuming  their  forms,  and  through  those  changes  by 
which  certain  of  the  fibrous  elements  are  derived  from 
them.  In  a  few  of  the  organs  of  the  adult  this  tissue 
seems  but  partially  developed,  notably  in  the  dental  pulp 
(see  fig.  16),  the  ground  substance  remaining  in  large 
proportion,  and  the  cells  being  developed  with  but  slight 
inter-mixtures  of  the  fibrous  elements.  These  have  been 
termed  myxomatous  tissues.  But  generally  the  tissues 
undergo  such  development  as  to  completely  change  their 
apparent  character.  The  ground  substance  disappears 
more  or  less  completely,  giving  place  to  fibers  of  various 
forms.  Among  these,  two  varieties,  differing  essentially 
the  one  from  the  other  appear,  known  as  the  white  and 
the  yellow,  or  the  inelastic  and  the  elastic  fibers.  The 
former  is  in  much  the  larger  proportion,  and  its  develop- 
ment is  traced  very  directly  from  the  primary  cells  found 
in  the  basis  substance. 

In  fig.  1,  I  present  an  illustration  of  the  tissue  taken 
from  beneath  the  epithelium  of  the  abdominal  wall  of  a 
human  fetus  in  the  sixth  week,  and  in  fig.  2,  a  specimen 
from  the  same  locality  from  a  little  older  fetus.  (The 
umbilical  cord  is  usually  recommended  for  obtaining 
views  of  embryonic  tissues.)  In  fig.  1,  the  cells  are  round, 
oblong  or  irregular  in  form  and  the  cell  contents  slightly 
granular,  and  presenting  either  no  clearly  defined  nucleus, 
or  it  appears  but  faintly,  or  at  least  it  has  not  the  prorni- 


TISSUE   ELEMENTS   AND    DISTRIBUTION.  9 

nence  seen  in  the  epithelia.  In  fig.  2,  the  cells  are  gen- 
erally assuming  a  lengthened  form  in  a  common  direction, 
and  some  of  them  present  pointed  extremities,  yet  no  true 
fibers  are  present. 

In  fig.  3,  the  cells  are  illustrated  in  a  more  fully  devel- 
oped state,  in  which  the  points  are  drawn  into  long 
slender  filaments.  These  may  often  be  found  in  the  sub- 
cutaneous tissue  of  the  fetus,  lying  side  by  side  and  end 
to  end  with  their  filaments  joined  together,  apparently,  in 
such  relative  position  that  the  full  length  of  the  filaments 
of  two  cells  lie  side  by  side,  as  in  the  two  lower  cells  in 
fig.  3.  Sometimes  these  fibers  seem  to  be  fused  into  one* 
As  the  development  proceeds  this  appearance  is  changed 
by  the  development  of  numerous  fibers  between  the  cells  ; 
the  cells  meanwhile  becoming  smaller.  As  to  the  precise 
mode  of  the  formation  of  these  fibers  there  is  still  some 
difference  of  opinion  among  histologists.  One  view  re- 
gards them  as  developed  from  the  ground  substance  in 
the  immediate  neighborhood  of  the  cell,  and  another, 
that  the  fiber  is  shed  out  from  the  cell  itself — is  the  direct 
product  of  the  cell.  One  can  hardly  trace  this  develop- 
ment as  it  proceeds  without  feeling  a  conviction  that  the 
fibers  arise,  at  least,  under  the  immediate  supervision  of 
the  cell.  I  shall,  therefore,  call  such  cells  fibroblasts. 
This  fibrillation  proceeds  until  the  ground  substance  has 
disappeared  and  given  place  to  a  fibrous  tissue  which  pre- 
sents the  appearance  represented  in  fig.  4.  As  the  tissue 
grows  older  the  cells  are  separated  more  and  more  widely, 
and  become  smaller,  until  finally  in  the  older  tissues  they 
are  represented  only  by  thin  scales  lying  among  the  fibers. 
Many,  and  often  almost  all  of  them,  disappear  entirely. 
This  disappearance  is  often  quite  complete  in  the  more 
compact  fibrous  tissues,  especially  the  tendons.  In  the 
developed  tissue  the  fibers  are  generally  not  straight  un- 
less put  upon  the  stretch,  but  pursue  a  wave-like  course, 
as  shown  in  fig.  5. 
2 


10  TISSUE   ELEMENTS    AND    DISTRIBUTION. 

These  fibers  are  very  small,  and  are  usually  gathered 
together  in  bundles  in  which  the  individual  fibers  may 
seem  to  have  but  slight  connection  with  each  other,  and 
form  broad,  flattened,  wavy  belts  of  loose  texture,  running 
parallel  or  crossing  each  other  in  various  directions,  as  in 
the  peridental  membrane,  or  may  be  formed  in  close,  com- 
pact bundles,  that  assume  the  form  of  large  fibers  (coarse 
fibers — fig.  6),  running  nearly  parallel,  but  interlocking 
with  each  other,  as  in  the  outer  layers  of  the  periosteum, 
or  may  cross  each  other  in  every  conceivable  direction, 
leaving  larger  inter-spaces  or  meshes  (areolse)  between 
them,  as  in  the  areolar  tissue,  or  may  be  compacted  into 
a  dense,  tangled  mass,  as  in  the  gums.  In  some  of  these 
forms  the  fibers  are  cemented  together  into  bundles  by  an 
intervening  substance. 

The  individual  fibers  are  never  seen  to  branch  or 
divide,  and  we  may  often  search  the  tangled  nets  of  the 
coarse  fibers  or  bundles  in  vain  to  find  them  dividing,  but 
in  some  localities  these  are  found  abundantly,  as  in  the 
gingivse.  These  branchings  are,  I  believe,  always  effected 
by  the  splitting  off  of  a  portion  of  the  fibers,  which  form 
a  bundle,  or  coarse  fiber,  as  represented  in  fig.  6  (from  a 
silver  nitrate  preparation).  The  smaller  bundles  which 
split  off  in  this  way  sometimes  join  and  form  a  part  of  an- 
other coarse  fiber,  and  by  these  divisions  and  junctions 
form  nets  through  which  fibers  running  in  different  direc- 
tions may  pass,  or  they  may  inclose  cellular  elements. 
This  kind  of  branching  occurs  perhaps  only  in  the  softer 
forms  of  the  coarse  fibers.  Occasionally,  when  the  tissue 
is  passing  from  a  more  firm  to  a  looser  texture,  the  more 
solid,  coarse  fibers  are  seen  to  break  up  and  spread  out  in 
finer  fibers,  as  represented  in  fig.  7. 

These  coarse  fibers  are  seldom  round.  They  are  often 
seen  to  form  bundles  interlocking  with  each  other ;  often 
in  compact  masses.  These,  when  seen  in  cross  sections, 
present  exceedingly  irregular  forms  and  sizes  (fig.  8). 


TISSUE   ELEMENTS   AND   DISTRIBUTION.  11 

Fine  sections  of  the  tissue  of  the  gums,  when  deli- 
cately stained  with  silver  nitrate  or  osmic  acid,  give  a 
great  variety  of  views  of  these.  In  this  position  the 
coarse  fibers  are  very  closely  interwoven,  and  every  field 
will  present  cross  sections  differing  in  outline  and  config- 
uration of  the  cut  ends  of  the  fibers. 

In  some  positions,  however,  we  find  branching  fibers 
of  a  different  type.  The  cells,  in  their  development, 
instead  of  assuming  the  tapered  spindle  forms,  with  pro- 
cesses at  either  end,  present  irregular  star  forms,  sending 
out  three  or  more  filaments,  as  represented  in  fig.  11.  In 
some  positions  these  cells  are  seen  to  remain  in  this  form 
without  further  fibrillation,  as  in  the  dental  pulp ;  but  in 
others,  notably  in  the  framework  of  the  lymphatic  glands, 
they  form  by  their  'fibrillation  an  intimately  branched  net- 
work, as  represented  in  fig.  9.  These  are  known  as 
reticular  fibers,  and  form  reticular  tissue.  In  these  the 
star-shaped  cells  are  seen  at  the  junction  of  the  branches, 
and  in  the  mature  forms  seem  to  lie  upon  them  as  a  flat- 
tened scale,  which  may  be  removed  by  brushing. 

These  fibers,  like  those  previously  studied,  are  not 
round.  The  shapes,  as  shown  in  cross  sections,  present 
indefinite  variation,  with  a  tendency  to  elongated  forms, 
as  illustrated  in  fig.  10,  showing  the  fibers  to  be  irregu- 
larly flattened. 

The  development  of  the  yellow  or  elastic  fibers  has  not 
been  traced  so  successfully  as  the  white,  and  there  is  still 
much  uncertainty  regarding  the  manner  of  their  origin. 
Krause  regards  them  as  being  developed  from  cells  in  a 
manner  similar  to  that  of  the  reticular  fibers,  except  that 
elastin  is  formed  instead  of  the  glue-giving  substance  of 
the  white  fibers.  Boll  and  others  have  also  traced  their 
formation  from  cells.  But  a  large  number  of  those  who 
have  examined  the  subject  have  failed  to  trace  the  devel- 
opment of  these  fibers  from  cells. 

Others  have  thought  that  elastic  fibers  are  developed 


12  TISSUE   ELEMENTS    AND   DISTRIBUTION. 

by  the  formation  of  granules  of  elastin  in  the  basis  sub- 
stance, and  the  union  of  these,  end  to  end.  The  same 
material  is  also  found  in  the  form  of  a  very  thin,  elastic, 
and  apparently  perfectly  homogeneous  membranes,  which 
are  supposed,  according  to  this  view,  to  arise  by  the  union 
of  the  granules  of  elastin  in  the  form  of  sheets,  which  be- 
come united  into  a  continuous  membrane. 

The  elastic  fibers  are  found  in  almost  all  parts  of  the 
soft  tissues  of  the  body,  except  the  epithelial  structures. 
In  another  form  this  substance  may  be  demonstrated  here 
also,  serving  as  a  connecting  substance  for  the  epithelium. 
If  a  very  thin  section  of  the  stratified  epithelium  be 
treated  with  a  33  per  cent,  solution  of  caustic  potash,  by 
the  plan  discussed  later  for  the  demonstration  of  elastic 
fibers,  the  epithelial  cells  will  gradually  disappear,  leav- 
ing a  delicate  net  of  elastic  material,  which  accurately 
represents  the  former  junctions  of  the  cells.  A  few  liga- 
ments are  composed  of  elastic  fibers  almost  as  pure  as  the 
ligamentum  nuchse  of  the  ox,  and  ligamentum  subflava  of 
man  ;  but  in  most  places  they  are  but  scantily  distributed. 
Wherever  found,  they  present  the  same  characteristic 
form  of  network.  The  fibers  divide  dichotomously  and 
form  junctions  freely,  and  in  this  form  are  interwoven 
with  the  white  fibers  of  the  areolar  tissues  and  the  fibrous 
membranes  ;  and  wherever  we  find  these  of  loose  texture, 
we  find  large  intermixtures  of  the  yellow  fibers.  I  have 
represented  in  fig.  12,  a  portion  of  these  nets  as  seen  at 
the  points  of  reflection  of  the  mucous  membrane  of  the 
lips  from  the  gums.  It  is  a  little  unusual,  in  the  fact  that 
it  represents  nodal  points  from  which  several  fibers  radi- 
ate, while  usually  they  divide  only  dichotomously,  as  rep- 
resented in  fig.  13. 

The  point  of  reflection  of  the  mucous  membrane  from 
the  gum  tissue  at  the  labial  side  of  the  teeth,  is  a  very 
good  place  to  study  them.  Here  the  tissue  is  of  a  very 
loose  structure,  and  the  mucous  membrane  is  united  to 


TISSUE   ELEMENTS   AND   DISTRIBUTION.  13 

the  parts  beneath  by  a  fine  network  of  elastic  fibers. 
Carmine  or  hematoxylin  stainings,  mounted  in  glycerine, 
serve  the  purpose  best  when  the  networks  are  sought ; 
but  for  examining  cross-sections  of  these  fibers  as  they 
occur  entwined  among  the  coarse  white  fibers,  osmic  acid 
or  silver  nitrate  stainings,  mounted  in  balsam,  give  bet- 
ter results  (fig.  15).  In  fig.  13,  I  have  represented 
the  fibers  as  they  appear  when  teased  out  from  elastic 
tendon. 

Elastic  fibers,  like  the  other  varieties,  are  seldom 
round.  In  fig.  15,  I  have  illustrated  these  forms  as  seen 
in  cross-section  in  a  silver  nitrate  staining,  in  a  group 
noticed  passing  between  some  coarse  white  fibers.  Elastic 
fibers  show  a  peculiar  disposition  to  curl  at  the  ends  when 
cut  or  broken,  which  1  have  represented  in  fig.  14,  giving 
examples  taken  from  the  position  mentioned  above.  Here 
we  will  often  see  the  short  pieces  cut  off  in  thin  sections, 
very  much  curled. 

The  cellular  elements  of  the  fibrous  membranes,  other 
than  those  already  described,  are  mostly  peculiar  to  the 
position,  rather  than  to  the  fibrous  tissue,  and  belong  to 
the  tissue  invested  rather  than  to  the  fibrous  investment, 
and  their  consideration  belongs  to  the  regional  descrip- 
tions. The  leucocyte  is  found  among  the  meshes  of  these 
membranes  very  generally,  and  other  cells  have  been 
described  as  especially  belonging  to  them  ;  particularly  a 
round,  nucleated  cell  larger  than  the  leucocyte,  and  cer- 
tain forms  of  the  branched  corpuscles.  In  some  positions 
these  latter  appear  abundantly,  notably  in  the  membranes 
of  the  eye.  It  seems  probable  that  some  of  these  are 
developmental  types  destined  for  some  use  in  the  neigh- 
borhood, rather  than  belonging  specifically  to  the  connec- 
tive tissues  as  such.  There  are,  however,  young  cells 
present  undergoing  development  in  perhaps  all  of  the 
tissues  of  young  animals,  and  possibly  in  the  old,  that,  in 
the  regeneration  or  augmentation  of  the  tissue,  pass  through 


14  TISSUE  ELEMENTS   AND   DISTRIBUTION. 

the  phases  already  described.  And  it  is  also  probable 
that  many  of  the  peculiar  forms  occasionally  seen  are  cells 
that  have  become  stationary,  have  begun  to  retrograde, 
or  have,  from  peculiarities  of  environment,  assumed  modi- 
fied forms. 

Fatty  tissue  consists  of  connective  tissue  cells,  filled 
with  oil,  which  usually  lie  heaped  together  in  little 
groups,  or  may  form  great  masses  by  aggregations  of 
these.  It  is  most  abundant  in  areolar  tissues  of  loose 
texture,  but  is  occasionally  found  in  the  fibrous  mem- 
branes. 

The  fibrous  membranes  act  very  largely  as  a  depot  of 
supplies  to  the  tissues  which  they  invest.  They  bear  the 
bloodvessels  and  nerves,  and  in  some  cases  they  receive, 
partially,  as  in  the  periosteum  for  the  bones,  and  in  others 
wholly,  as  in  the  peridental  membrane  for  the  cementum, 
the  pabulum  from  the  blood  to  be  transmitted  through 
their  meshes  to  the  point  of  assimilation. 

The  local  characteristics  of  the  individual  membranes 
are  continually  modified  by  the  deflection  of  their  fibers 
this  way  or  that,  to  give  place  for  the  passage  of  blood- 
vessels and  nerves,  and  for  the  investment  of  them.  These 
deflections  are  often  of  such  a  character  as  to  mislead  the 
observer  if  only  one  or  two.  sections  are  examined. 

In  these  forms,  and  inclosing  in  the  meshes  formed  by 
its  fibers,  varying  numbers  and  forms  of  cellular  elements, 
this  tissue  is  distributed  throughout  the  body.  It  is  con- 
tinuous everywhere,  and  has  been  described  by  different 
writers  under  a  great  variety  of  names,  according  to  the 
local  peculiarity  of  the  tissue  and  the  positions  in  which 
it  is  found.  It  is  fo.und  under  the  mucous  membranes  — 
submucous  tissue  ;  under  the  serous  membranes  —  sub- 
serous  tissue;  under  the 'skin  —  subcutaneous  tissue  ;  and 
about  the  bloodvessels  it  forms  a  continuous  membranous 
sheath,  or  investment,  and  in  this  way  gives  them  sup- 
port and  protection.  In  the  same  way  it  forms  the 


TISSUE   ELEMENTS   AND   DISTRIBUTION.  15 

investment  of  the  nerves  —  neurilemma  ;  and  incloses 
each  muscle  in  a  distinct  sheath  —  myolemma ;  and  dip- 
ping in  between  the  muscular  fibers,  surrounds  each  one 
individually  —  sarcolemma  ;  and  serves  to  connect  them 
with  their  tendons,  or  with  the  periosteum.  It  invests 
the  glands,  holding  their  lobes  in  position,  and,  following 
the  ducts  into  the  substance  of  the  gland,  forms  an  invest- 
ment for  each  lobule,  and  within  this  substance  the  blood- 
vessels that  supply  the  gland  ramify.  It  forms  the 
support  for  the  organs  of  the  hollow  viscera  —  peritone- 
um —  pleura  ;  it  invests  the  brain  —  dura  mater  — 
arachnoid  membrane,  and  forms  the  investment  or  ma- 
trix for  its  functioning  cells  —  neuroglia  ;  it  incloses  the 
heart  in  a  closed  sac  —  pericardium  —  and  forms  the 
investment  of  the  eye  —  sclerotica.  In  strong  membran- 
ous sheets —  fascia  —  it  binds  down  the  muscles,  and  holds 
them  in  position  ;  it  forms  the  investment  of  the  bones  — 
periosteum  —  and  serves  to  attach  the  roots  of  the  teeth 
to  their  alveoli — peridental  membrane.  In  a  still  more 
condensed  form  in  which  the  fibers  lie  parallel  with  each 
other,  it  forms  the  tendons  which  connect  the  muscles 
with  the  bones,  and  the  ligaments  which  connect  the 
bones  together. 

This  tissue  also  stands  in  very  close  developmental 
relations  with  still  other  and  seemingly  very  different 
tissues.  Cartilage  and  the  bones  are  developed  directly 
from  a  connective  tissue  matrix,  and  seemingly  the  one  is 
developed  from  the  other,  though  close  examination  seems 
to  reveal  the  fact  that  the  development  of  the  one  dis- 
places the  other  wholly  or  in  part.  The  bones,  at  least, 
are  developed  from  specialized  cells  —  the  osteoblasts, 
which  seem  endowed  with  a  special  bone-forming  power. 
These  cells  are,  however,  developed  from  connective 
tissue  cells,  or  at  least  from  the  cells  that,  from  all  that 
has  as  yet  been  learned  of  them,  are  the  same  as  the  em- 


16  TISSUE   ELEMENTS   AND   DISTRIBUTION. 

bryonal  connective  tissue  cells.    This  point  will  be  exam 
ined  more  particularly  later. 

It  appears  also  from  the  teachings  of  comparative  his- 
tology that  one  of  these  tissues  may  be  substituted  by 
another  of  equivalent  value.  That  which  in  one  animal 
appears  as  ordinary  connective  tissue  may  in  another  be 
of  quite  a  different  reticular  type  ;  and  that  which  is  rep- 
resented by  cartilage  in  one  may  be  substituted  by  bone 
in  another.  These  changes  are  often  icmarked  also  in 
the  developmental  stages  of  the  same  animal.  Thus  in 
mammals  the  greater  part  of  the  skeleton  is  first  repre- 
sented in  cartilage,  which  is  afterwards  replaced  by  bone, 
while  a  few  of  the  bones,  as  the  cranial,  are  first  repre- 
sented as  fibrous  membranes,  in  the  midst  of  which  the 
bones  are  formed.  This  is  called  the  inter-membranous 
formation  of  bone.  Three  modes  of  the  formation  of 
bone  are  usually  recognized;  the  inter -cartilaginous, 
inter-membranous,  and  the  sub-periosteal. 

Further  than  this  these  tissues  have  other  relation- 
ships from  a  physiological  point  of  view.  Their  signifi- 
cance in  the  action  of  the  healthy  body  is  of  a  more 
subordinate  kind ;  though  they  make  up  an  enormous 
proportion  of  it.  They  represent,  as  is  usually  said, 
tissues  of  lower  vital  dignity  (Frey),  and  seem  in  a 
degree  subordinate  to  the  more  proper  functioning  tissue 
for  which  they  form  an  extended  framework  in  the 
meshes  or  cavities  of  which  the  muscles,  vessels,  nerves, 
gland  cells  and  organs  lie  imbedded. 

The  name  then  of  connective  tissue  seems  to  be  en- 
tirely appropriate.  If  we  farther  reckon  the  muscular 
tissue  with  this  group,  which  seems  proper  according  to 
most  histologists  from  its  developmental  relations  — 
though  it  is  widely  specialized,  —  it  may  aptly  be  termed 
the  tissue  of  support  and  motion,  while  the  tissues  of  the 
epithelial  type  constitute  the  tissues  of  function  and  pro- 
tection. 


CHAPTER  III. 

METHODS   OF   THE  PREPARATION   OF  TISSUES. 

Perhaps  it  would  be  well,  before  going  farther,  to 
indicate  briefly  the  methods  I  have  employed  in  the 
preparation  of  the  tissues  from  which  my  studies  and 
illustrations  of  those  to  be  described  have  been  made. 
These  have  been  taken,  for  the  most  part,  from  young  and 
small  animals,  such  as  the  cat,  lamb,  pig,  dog,  etc.  The 
human  fetus,  and  also  tissues  taken  from  the  adult,  have 
been  employed  in  sufficient  amount  to  make  reasonably 
good  comparisons,  but  the  difficulty  of  obtaining  these 
sufficiently  fresh  to  give  the  best  results,  is  quite  obvious. 
The  time  between  the  death  of  the  animal  and  the  im- 
mersion of  the  tissue  in  the  fluids  by  which  it  is  prepared 
for  cutting,  should  be  counted  by  minutes,  never  by  hours. 
For  this  purpose  I  have  used  Miiller's  fluid  and  chromic 
acid,  giving  the  preference  to  the  former,  and  have  usually 
added  the  acid  for  decalcification,  after  the  first  day.  It 
has  been  considered  important  that  very  small  bones  be 
used,  in  order  that  the  time  of  exposure  to  acids  in  the 
process  of  decalcification  be  as  short  as  possible.  It  is 
exceedingly  difficult  to  cut  large  bones  into  sufficiently 
small  pieces,  without  disturbing  the  relations  of  the  soft 
portions  of  the  tissue,  especially  in  the  loosely  attached 
portions  of  the  periosteum.  The  injurious  effect  of  acids 
has  been  closely  studied,  and  it  has  been  found  that  the 
element  of  time  is,  within  certain  limits,  more  important 
than  the  strength  of  the  acid  solution  employed  ;  -that  is 
to  say,  a  tissue  decalcified  in  one  day  with  a  three  per 
cent,  solution  of  nitric  acid,  and  then  thoroughly  de- 
acidulated  by  copious  ablution,  will  come  under  the  lens 

3  17 


18         METHODS   OF  THE   PREPARATION   OP  TISSUES. 

in  better  condition  than  if  exposed  to  one-half  per  cent, 
for  five  or  six  days. 

The  use  of  alcohol  in  hardening  has  been  avoided  as 
far  as  possible,  on  account  of  the  shrinkage  which  it  in- 
duces. Indeed,  it  has  been  limited  to  the  dehydration  of 
the  tissue  for  the  purpose  of  impregnation  with  the  im- 
bedding material,  in  cases  in  which  this  is  demanded. 
Some  sections  of  each  class  of  tissue  have  been  made 
without  dehydrati'on,  or  any  form  of  impregnation,  for 
purposes  of  comparison  and  the  formation  of  conclusions 
as  to  the  changes  induced  by  the  different  materials  used 
for  these  purposes.  By  this  mode  we  are  unable  to  obtain 
sections  sufficiently  thin  and  regular  for  general  study, 
but  may  obtain  scraps  that  will  reveal  the  tissue  charac- 
ters for  comparison.  Such  studies  demonstrate  that  all 
of  the  modes  of  impregnation  yet  used  for  the  purpose  of 
cutting  sections,  injure  the  tissues  in  some  degree,  and 
that  this  injury  is  very  closely  associated  with  the  time 
the  tissue  is  allowed  to  remain  in  the  imbedding  material. 
Of  these  I  have  used  gum  arabic,  celloidin,  bayberry  tal- 
low (the  concrete  expressed  oil  of  Laurus  hobilus,  or  bay- 
berry  tree),  paraffin,  and  paraffin  modified  by  additions 
of  cosmoline.  The  finest  sections  may  be  cut  in  paraffin. 
The  disposition  of  this  material  to  curl  up  before  the 
knife,  is  readily  avoided  by  laying  a  piece  of  fine  tissue 
paper  wet  with  alcohol  upon  it,  and  cutting  under  this. 
This  paper  also  serves  well  to  transfer  the  sections  to 
fluids.  The  necessary  subjection  of  the  tissue  to  alcohol 
for  dehydration,  then  to  warm  chloroform  in  the  impreg- 
nation of  the  tissue,  and  the  removal  of  the  paraffin  after 
cutting,  is  not  without  evil  result.  In  this  respect  the 
bayberry  tallow  is  better,  as  the  use  of  chloroform  is 
avoided,  warm  alcohol  being  sufficient  both  for  impregna- 
tion, and  solution  and  removal  of  the  tallow  after  cutting. 
Each  of  these  have  given  me  better  results,  as  to  the  final 
Condition  of  the  tissue,  than  the  celloidin ;  but,  in  order 


METHODS   OF  THE   PREPARATION   OP  TISSUES.         19 

to  obtain  good  results,  the  time  the  tissue  remains  in  the 
imbedding  material  must  only  be  counted  by  minutes, 
never  by  hours ;  and  if,  after  its  removal,  and  placing  the 
tissue  in  water,  it  does  not  swell  out  to  its  normal  propor- 
tions in  every  part,  which  failure  may  be  detected  after 
sufficient  experience  by  its  appearance,  it  should  be  cast 
aside  and  a  new  effort  made.  The  gum  arabic  method  is 
suitable  only  for  very  small  bits  of  tissue,  on  account  of 
the  time  necessary  for  hardening  large  masses.  Tissue 
may  be  bound  up,  or  shrunken  in  any  of  these  processes 
for  a  very  short  time,  without  losing  its  resiliency,  or 
power  of  resuming  its  original  condition,  but  if  it  is  con- 
tinued beyond  a  certain  time,  this  is  lost  in  a  greater  or 
less  degree.  Careful  additions  of  acetic  acid  to  the  water 
will  often  assist  in  the  restoration  of  the  normal  condi- 
tion of  the  tissue.  The  ordinary  microtome  has  been  used 
for  cutting  sections.  The  staining  has  been  by  carmine 
in  its  different  forms,  Picrocarmine,  hematoxylin,  osmic 
acid,  and  chloride  of  gold.  Double  stains  of  carmine  and 
hematoxylin,  and  pigmenting  (see  below)  have  been  made 
use  of.  Sections  from  each  portion  of  tissue  cut  have 
been  studied,  mounted  in  glycerine  jelly,  plain,  also  plain 
after  acetic  acid,  and  in  each  of  the  above  stains,  and  then 
these  studies  repeated  in  similar  mountings  in  balsam. 
The  aniline  dyes  have  been  tried  in  tissues  in  which  acids 
have  been  used  to  decalcify  bones,  but  have  not  given  me 
good  results. 

Pigmentation  should  be  explained,  as  I  do  not  know 
af  the  use  of  the  process  by  others.  It  is  done  in  two 
ways,  making  a  diffusive  or  selective  pigmentation  as  de- 
sired. Place  the  sections  in  osmic  acid  solution  (one  per 
cent.),  and  let  them  remain  from  half  an  hour  to  an  hour. 
(1st.)  Transfer  to  distilled  water  for  half  a  minute,  just 
long  enough  to  remove  the  osraic  acid  from  the  surface, 
and  at  once  place  in  a  solution  of  hematoxylin,  as  pre- 
pared for  staining — a  thin  solution  is  best — and  allow 


20         METHODS   OF  THE  PREPARATION  OF  TISSUES. 

them  to  remain  until  they  have  assumed  a  deep  smoke  or 
soot  color,  which  will  require  but  a  few  minutes.  (2d.) 
Wash  thoroughly  in  distilled  water  from  half  an  hour  to  an 
hour,  then  transfer  to  solution  of  hematoxylin  as  before. 
The  change  to  the  soot  color  will  be  a  little  slower.  Any 
purple  color  acquired  from  this  solution  may  be  removed 
by  acetic  acid  without  affecting  the  pigment.  The  sec- 
tions may  now  be  prepared  and  mounted  in  any  manner 
desired,  and  will  be  found  very  transparent  to  transmitted 
light,  provided  the  pigmenting  has  not  been  carried  too 
far.  In  (1st)  the  pigmenting  will  effect  all  the  tissues 
alike,  is  diffusive,  but  in  such  a  way  that  all  of  the  ele- 
ments come  fairly  into  view.  In  ("2d)  the  pigmenting  is 
selective,  the  osmic  acid  resisting  removal  by  water  is  re- 
duced as  pigment  by  the  hematoxylin.  This  pigmenting 
rests  on  the  fact  that  a  mixture  of  osmic  acid  and  hema- 
toxylin throws  down  an  amorphous  black  deposit,  and  this 
is  obtained  in  the  tissue  in  such  a  fine  state  of  division  as 
to  resemble  a  stain  when  the  highest  powers  of  the  micro- 
scope are  used.  Some  portions  of  the  tissue  hold  the 
osmic  acid — at  least  do  not  give  it  up  to  water  very 
readily — hence  the  selective  pigmenting  of  the  tissues 
that  are  well  washed  after  removal  from  the  acid,  before 
being  submitted  to  the  hematoxylin.  In  this  way,  ordi- 
nary epithelium  may  be  made  to  resemble  natural  pig- 
ment cells,  the  cell  body  being  pigmented  deeply,  while 
the  nuclei  and  cementing  substance  remain  transparent. 
A  word  as  to  the  illustrations.  These  are  all  made 
from  tissues  freshly  prepared  for  the  study  of  this  subject, 
and  are  done  with  as  much  care  as  to  accuracy  of  repre- 
sentation as  I  have  been  able  to  bestow.  The  manner  of 
the  representation  of  the  tissues  generally  emploj^ed,  is  in 
a  large  degree  conventional,  and  my  illustrations  are  no 
exception  to  the  rule.  That  which  I  have  made  out  to 
my  own  satisfaction,  I  have  endeavored  to  represent 
clearly,  avoiding  the  representation  of  either  shadows  or 


METHODS   OF  THE  PREPARATION   OF  TISSUES.         21 

suppositions.  I  therefore  make  no  claim  that  the  pictures 
are  exact  representations  of  individual  fields  in  my  sections, 
but  are  rather  what  I  make  out  to  be  the  actual  forms  of 
the  tissue  elements  and  their  relations  to  each  other,  after 
having  made  the  best  study  of  them  that  I  am  able  to  do 
at  the  present  time. 


CHAPTER  IV. 

THE   PERIOSTEUM. 

The  periosteum  forms  the  immediate  covering  of  the 
bones.  It  is  continuous  at  all  points  except  those  surfaces 
covered  by  the  articular  cartilages  and  the  attachment  of 
the  ligaments  and  tendons. 

It  is  not,  therefore,  continuous  from  bone  to  bone,  ex- 
cept in  those  united  by  suture,  as  the  cartilages  men- 
tioned uniformly  clothe  the  ends  of  those  united  by  joints. 
Each  of  the  long  bones,  and  most  of  the  short  ones  also, 
has  its  individual  periosteum,  which  encloses  it  as  in  a 
sack,  and  is  closely  adapted  to  all  parts  of  its  surface. 

If  the  flesh  is  carefully  removed  from  any  of  the  long 
bones  the  periosteum  will  be  seen  to  present  a  smooth, 
white,  lustrous  appearance,  much  like  the  surface  of  a 
tendon,  over  a  large  part  of  the  surface,  but  at  certain 
points  which  correspond  with  the  attachment  of  muscles, 
or  fascia,  it  will  be  left  more  or  less  ragged  and  dull,  for 
at  such  points  the  superimposed  tissues  are  firmly  adherent 
and  must  be  cut  away  with  the  knife.  At  all  other  places 
the  tissues  separate  from  it  easily  and  smoothly,  indeed, 
are  not  attached,  or  are  attached  only  by  a  very  slight 
network  of  reticular  or  elastic  fibers  which  break  away 
readily  and,  to  the  naked  eye,  leave  no  sign  of  their  pres- 
ence. If  now  we  slit  up  the  periosteum  lengthwise  the 
bone,  along  a  smooth  portion,  and  insert  the  handle  of  the 
scalpel  beneath  it,  it  will  be  found  readily  separable  from 
the  bone  over  the  greater  part  of  its  surface.  Indeed,  the 
attachment  seems  to  be  but  little  more  intimate  than  was 
that  of  the  tissues  to  the  outer  surface.  However,  if  the 

22 


THE   PERIOSTEUM.  23 

detachment  be  closely  followed  it  will  be  seen  that  at 
many,  or  perhaps  only  a  few  points,  fibers  adhere  to  the 
bone,  and  are  broken.  These  are,  in  the  main,  very  small 
blood  vessels  that  enter  the  bone  from  the  periosteum,  but 
occasionally  a  few  fibers  of  the  periosteum  enter  the  bone 
also. 

In  the  progress  of  the  detachment  a  point  is  arrived  at 
finally  where  this  easy  separation  ceases  abruptly,  and  the 
periosteum  becomes  firmly  adherent  to  the  bone.  It  is 
now  found,  in  the  effort  to  continue  the  detachment,  that 
the  periosteum  is  a  very  thin,  tough,  inelastic  membrane 
that  is  torn  with  difficulty,  but  it  is  impossible  to  continue 
the  separation  from  the  bone  otherwise  than  with  the 
knife,  and  the  extreme  thinness  of  the  membrane  renders 
this  difficult.  An  examination  of  these  adherent  points 
reveals  the  fact  that  they  are,  first:  points  at  which 
some  of  the  tissues  are  attached  to  the  outer  surface 
of  the  periosteum,  as  muscles  or  fascia ;  second,  near 
the  ends  of  the  bones  where  the  periosteum  approaches 
the  articular  cartilages ;  third,  wherever  it  approaches  the 
insertion  of  tendons  or  ligaments  ;  fourth,  wherever  mu- 
cous membranes,  or  the  skin,  seems  adherent  to  the  bones 
beneath,  as  at  the  entrance  of  the  meatus  auditorius,  the 
gums,  mucous  membrane  of  the  nose,  etc.  At  all  such 
points  the  periosteum  is  as  firmly  adherent  to  the  bone  as 
if  it  formed  an  integral  portion  of  it,  and  serves  as  the 
medium  or*  attachment  for  the  superimposed  tissues. 
Through  this  medium  many  attachments  of  muscles, 
fascia,  etc.,  are  effected,  and  these  points  of  attachment 
will  intercept  and  prevent  the  separation  of  the  periosteum 
from  the  bones  at  many  points.  This  feature  of  the  an- 
atomy of  the  periosteum  has  not  yet  been  studied  in  detail. 
Yet  its  importance  in  the  management  of  diseases  of 
the  bones,  especially  the  suppurative  diseases,  when  pus 
is  likely  to  find  its  way  beneath  the  loosely  attached  per- 
iosteum, must  be  apparent  to  every  surgeon.  While  I 


24  THE   PERIOSTEUM. 

can  not  now  undertake  this  part  of  the  subject  in  extenso^ 
I  propose  on  another  page  to  consider  very  closely  the 
character  of  the  attachments  of  the  periosteum  at  differ- 
ent points. 

Histologically ,  the  periosteum  is  composed  of  fibrous 
tissue,  in  the  meshes  of  which  are  found  certain  cellular 
elements.  It  presents  for  examination  : 

1st.    An  outer  layer  of  coarse  white  fibrous  tissue. 

2nd.  An  inner  layer  of  fine  white  fibrous  tissue. 

3rd.   Elastic  fibers. 

4th.  Pentrating  fibers,  or  fibers  of  the  periosteum  that, 
in  the  growth  of  the  bone,  are  included  in  its  substance. 
(Fibers  of  Sharpey.) 

5th.  Osteoblasts,  or  a  layer  of  cells  that  lie  between 
the  periosteum  and  the  bone. 

6th.   Osteoclasts — cells  that  absorb  bone. 

The  white  fibrous  tissue  is  everywhere  disposed  in  two 
layers,  an  inner  and  an  outer ;  or  a  layer  of  coarse  fibers 
forming  the  outer  portion,  and  a  layer  of  fine  fibers  form- 
ing the  portion  next  to  the  bone.  The  yellow  or  elastic 
fibers  are  found  mostly  intermingled  with  the  coarse 
fibrous  layer.  They  are  usually  very  difficult  of  observa- 
tion, and  do  not,  as  a  rule,  appear  in  sections  as  ordinarily 
prepared . 

OUTER   LAYER. 

The  size  and  arrangement  of  the  coarse  fibers  in  the 
formation  of  the'  outer  layer  is  exceedingly  variable  in 
different  regions  of  the  osseous  system.  On  the  long 
bones  they  are  generally  smaller  than  upon  the  short, 
while  I  have  found  the  largest  fibers  about  the  bones  of 
the  face.  The  rule  is  that  the  periosteum,  as  a  whole,  is 
thicker  and  stronger  at  exposed  points  where  the  bones 
are  near  the  surface,  and  is  more  delicate  when  deeply 
covered  with  other  tissues.  Hence  we  find  it  thin,  and 
its  fibers  correspondingly  delicate  on  the  shafts  of  the 
long  bones,  especially  such  as  the  femur,  humerus,  etc. 


THE  PERIOSTEUM.  25 

In  these  positions  the  coarse  fibers  of  the  outer  layer 
are  small,  and  for  the  most  part  run  parallel  with  the  long 
axis  of  the  bone.  (See  fig.  17.)  The  fibers  are  usually 
very  much  flattened,  and  the  fine  fibers  of  which  they  are 
formed,  not  very  firmly  bound  together.  Indeed,  they 
are  often  disposed  in  ribbon-like  layers,  with  the  flat  sides 
horizontal  to  the  surface  of  the  bone,  and  the  edges  of 
these  are  often  joined  in  such  a  manner  as  to  form  a  con- 
tinuous sheet  of  fibrous  material.  This  is  especially  the 
case  when  the  periosteum  is  deeply  covered  with  muscles 
which  perform  sliding  motions  on  its  surface.  In  such 
places  this  portion  is  often  made  up  of  a  number  of  lamel- 
lae thus  formed,  which  are  very  loosely  joined  together,  so 
that  by  careful  manipulation  it  may  be  separated  into  a 
number  of  complete  lamellae.  The  fibers  which  constitute 
these  layers  do  not  all  run  in  the  direction  of  the  long  axis 
of  the  bone,  but  some  are  interposed  which  cross  these  at 
right  angles,  or  in  the  direction  of  the  circumference  of 
the  bone,  as  shown  in  fig.  18,  in  a  section  cut  lengthwise, 
from  the  tibia  of  the  pig.  This  example  shows  five  layers 
of  circumferential  fibers,  and  those  marked  /  and  i,  have 
shifted  from  their  position  in  mounting  the  section  in  such 
a  way  as  to  present  the  sides  of  short  sections  to  view,  in- 
stead of  the  ends,  and  serve  well  to  show  how  the  fine 
fibers  are  joined  into  ribbon-like  forms.  The  figure,  as  a 
whole,  illustrates  how  readily  the  different  layers  are 
separable,  though,  as  combined,  they  are  calculated  to 
give  great  strength,  at  the  same  time  accommodating 
sliding  movements  readily. 

I  have  endeavored  to  represent  every  portion  of  it  just 
as  it  happened  to  lie  in  the  preparation.  This  may  be  re- 
garded as  an  example  of  the  more  complex  arrangement 
of  the  coarse  fibers,  or  outer  layer,  in  the  non-attached 
periosteum.  The  disposition  of  the  fibers  is  usually  much 
more  simple,  presenting  fewer  running  in  a  circumferen- 
tial direction  until,  finally,  none  whatever  can  be  found. 
4 


26  THE   PERIOSTEUM. 

This  simpler  form  I  have  represented  in  fig.  17,  from  a 
lengthwise  section  from  the  femur  of  a  kitten.  Every 
gradation  between  these  may  be  found.  For  this  illus- 
tration a  point  has  been  selected  where  the  outermost 
fibers  have  been  broken  by  the  needle  in  detaching  the 
superimposed  tissue.  Some  of  the  fibers  beneath  are  also 
a  little  separated,  and  in  the  central  part  the  layer  of 
osteoblasts  is  pulled  partly  away  from  the  bone,  display- 
ing their  processes  to  advantage.  It  will  be  seen  that  the 
fine  fibers,  a,  cease  abruptly,  giving  place  to  the  coarse 
fibers  of  the  outer  layer  c.  By  comparing  this  illustra- 
tion with  fig.  21,  and  noting  the  difference  in  the  size  of 
the  osteoblasts  (for  the  illustrations  are  drawn  with  dif- 
ferent powers)  some  idea  will  be  gained  of  the  difference 
in  the  size  of  the  coarse  fibers  in  different  regions.  In 
drawing  fig.  17,  the  ^-inch  immersion  lens  was  used, 
while  in  fig.  21  the  J-inch  dry  was  substituted.  These 
fibers  (fig.  17)  are  round  or  irregularly  flattened,  and  show 
none  of  the  ribbon-like  forms  seen  in  fig.  18.  It  is  the 
form  of  this  layer  most  commonly  met  with  on  the  shafts 
of  the  long  bones,  though  the  gradations  between  these 
two  figures  are  sufficiently  common.  In  both  of  these 
figures  I  have  illustrated  the  delicate  reticular  tissue  by 
which  the  periosteum  is  very  loosely  attached  to  the  super- 
imposed parts. 

As  the  ends  of  the  bones  are  approached  the  perioste- 
um is  thinner,  and  often  the  coarse  fibrous  layer  is  found 
lying  almost  flat  on  the  bone,  most  of  the  inner  layer 
having  disappeared,  and  at  many  points  the  osteoblasts 
are  not  to  be  seen.  (Fig.  19.)  At  frequent  intervals, 
however,  sometimes  continuously  for  a  space,  osteoclasts 
(/././.)  have  taken  their  place,  and  are  trimming  down 
the  surface  of  the  enlarged  ends.  In  this  region  the  fibers 
of  the  periosteum  enter  the  bone  and  in  this  way  form 
the  firm  attachments  noticed  at  their  ends.  (Fig.  19.) 
This  happens  to  such  an  extent  that,  in  pursuing  the  study 


THE   PERIOSTEUM.  27 

of  sections  cut  lengthwise  the  shaft  of  the  bone,  up  to 
the  articular  cartilage,  one  is  impressed  with  the  idea  that 
the  whole  of  the  periosteum  has  sunk  beneath  the  surface 
of  the  bone.  As  this  occurs  the  fibers  of  the  outermost 
parts  of  the  coarse  fibrous  layer  often  seem  to  unite  into 
a  fibrous  sheet  which  is  inserted  finally  at  the  margin  or 
fringe  of  the  articulat  cartilage,  or  into  the  cartilage 
itself. 

On  the  bones  of  the  face  and  other  positions  where  the 
periosteum  lies  near  the  surface  of  the  tissues,  the  outer 
layer  is  composed  of  very  large,  white  fibers,  with  which 
a  small  quantity  of  yellow  elastic  fibers  is  mingled.  The 
white  fibers  form  an  intimate  network,  being  closely  in- 
terwoven with  each  other.  (See  figs.  20  D,  and  21  E.) 
Sections  cut  in  almost  any  direction  will  show  longitudinal 
fibers,  but  a  disposition  to  run  in  the  direction  of  the  pull 
or  strain  of  muscles  or  other  tissues  attached  to  the  peri- 
osteum may  be  seen  ;  otherwise  the  direction  will  have  a 
tendency  to  follow  the  long  axis  of  the  formation  of  the 
bone.  In  either  case  a  considerable  number  take  a  trans- 
verse or  a  diagonal  direction,  passing  through  the  meshes 
formed  by  the  principal  fibers.  None  of  these  fibers  take 
a  direction  perpendicular  to  the  surface  of  the  bone,  but 
they  are  so  disposed  that  a  fiber  that  may  be  on  the  inner 
surface  of  the  layer  at  one  point,  may  at  a  little  distance 
arrive  at  the  outer  surface.  In  this  way  the  fibers  seem 
to  be  plaited  together,  (fig.  21  E),  sometimes  in  a  very 
compact  layer  only  a  few  fibers  in  thickness,  and  some- 
times the  fibers  are  so  disposed  as  to  form  several  lamellae, 
held  together  by  occasional,  or  it  may  be  very  frequent, 
passage  of  fibers  from  the  one  layer  to  the  other,  or  by  a 
network  of  elastic  fibers  only.  (Fig.  22.)  Usually,  even 
in  cases  of  considerable  thickness  of  this  layer,  coarse 
fibers  may  be  traced  that  in  their  longitudinal  course 
gradually  approach  one  or  the  other  surface. 

The  thickness  of  this  layer  is  very  variable.     Occasion- 


28  THE  PERIOSTEUM. 

ally  it  is  only  the  thickness  of  two  or  three  coarse  fibers 
superimposed  on  each  other ;  rarely  the  coarse  fibrous, 
layer  is  condensed  into  a  single  membranous  sheet,  to 
which  the  overlying  tissues  are  attached.  On  the  other 
hand,  I  have  seen  the  thickness  of  J-inch  in  the  human 
subject ;  however,  I  am  not  sure  that  the  latter  was 
entirely  normal.  The  thinner  portions  are  often  those  to 
which  muscles  are  attached.  Indeed,  the  statement  is 
made  by  Krause  (Allgemeine  und  Microscopische  Anato- 
mic, p.  68)  that  this  layer  is  sometimes  wanting  at  the- 
points  of  attachment  of  muscles.  Although  I  have  made 
many  cuttings  through  such  points,  I  have  never  found 
this  layer  absent  except  when  the  muscle  was  attached 
to  the  bone  by  well-defined  tendon,  in  which  case  none 
of  the  elements  of  the  periosteum  whatever  remain,  but 
the  fibers  of  the  tendon  pursue  their  course  uninter- 
ruptedly into  the  surface  of  the  bone. 

The  characters  described  above  are  present  in  the 
coarse  fibrous  layer  of  the  periosteum  wherever  it  is 
found,  without  exception.  At  a  few  points  it  is  blended 
with  other  fibrous  tissues,  especially  with  the  mucous 
membranes  and  skin,  as  it  is  seen  in  the  gums,  and  at  the 
entrance  of  the  opening  of  the  external  ear,  and  other 
points  at  which  the  skin  is  rigidly  adherent.  In  these 
cases,  if  we  proceed  from  the  surface  of  the  bone  out- 
wards, the  first  coarse  fibers  are  always  disposed  as  in  the 
periosteum  at  other  points,  i.  e.,  lying  horizontal  to  the  sur- 
face of  the  bone  ;  but  after  passing  a  few  of  these,  the  hori- 
zontal direction  of  the  fibers  is  sometimes  gradually,  some- 
times abruptly,  lost,  and  the  character  of  the  tissue  changes 
to  the  tangled  fibrous  forms  of  the  skin,  the  gums,  areolar 
tissue,  or  whatever  may  be  the  superimposed  fibrous 
tissue. 

Often,  however,  the  periosteum  remains  entirely  dis- 
tinct from  the  superimposed  tissue,  and  is  united  with  it 
only  by  a  scanty  network  of  elastic  fibers  which  allow  of 


THE   PERIOSTEUM.  29 

free  sliding  motions  of  the  one  tissue  upon  the  other. 
All  grades  of  connection,  from  this  latter  to  the  intimate 
commingling  of  the  coarse  fibers,  may  be  found  in 
different  places.  Many  of  the  smaller  muscles,  and  larger 
ones  that  have  their  attachments  by  a  broad  base,  are 
attached  directly  to  this  layer  of  the  periosteum.  In  case 
of  the  muscles,  the  sarcolemma  of  each  individual  mus- 
cular fiber  is  attached  directly  to  these  coarse  fibers. 
(Figs.  20  and  21.)  In  a  few  cases  fine  fibers  may  be  seen 
traversing  the  layer  of  horizontal  fibers  of  the  periosteum 
in  a  perpendicular  direction,  seeming  to  be  condensed  ex- 
tensions of  the  sarcolemma  as  shown  in  Fig.  21.  Occa- 
ionally  these  pass  entirely  through  the  coarse  fibrous 
layer,  and  then  appear  to  be  continuous  with  the  fibers  of 
the  internal  layer.  The  fasciae  are  attached  to  the  perios- 
teum by  their  fibers  blending,  or  becoming  continuous 
with  those  of  its  external  layer. 

INTERNAL     LAYER. 

The  internal  layer  is  of  an  entirely  different  character 
from  the  outer,  both  in  the  nature  of  its  fibers  and  in 
their  arrangement.  It  also  presents  great  diversity  of 
arrangement.  In  the  consideration  of  this  layer  it  will 
be  convenient  to  divide  it  into  attached  and  non-attached, 
as  it  presents  notably  different  characters  in  its  fibrous 
structure,  and  in  the  relation  of  its  fibers  to  the  bone 
which  it  clothes. 

The  non-attached  inner  layer  of  the  periosteum  is 
separated  from  the  bone  almost  completely  by  an  inter- 
vening layer  of  polygonal  or  flattened  cells,  the  osteo- 
blasts.  (Figs.  17  and  18).  None  of  its  fibers  pass  into 
the  bone ;  while  in  the  attached  periosteum  those  of  the 
inner  layer  do  pass  into  it,  or  seem  to  spring  out  of  it. 
(Figs.  21,  23  and  24.)  It  is  composed  of  the  finest  and 
most  delicate  white  connective  tissue  fibers,  with  which 
there  are  no  coarse  white,  or  yellow  elastic  fibers  asso- 


30  THE   PERIOSTEUM. 

elated.  On  the  short  bones  these  fibers  seem  not  to  be 
disposed  in  any  particular  direction,  or  upon  any  specific 
plan  that  I  have  been  able  to  detect.  They  decussate 
freely  in  every  direction.  On  the  long  bones  the  fibers 
of  this  layer  are  more  generally  parallel  to  the  long  axis 
of  the  bone,  as  illustrated  in  fig.  21,  though  not  uni- 
versally so.  In  all  young  animals  these  have  in  their 
meshes  a  considerable  number  of  young  connective  tissue 
cells  in  various  stages  of  development,  in  addition  to  the 
fusiform  nuclei  of  the  white  fibrous  tissue  or  fibroblasts. 
In  the  main  the  fibers  lying  next  to  the  layer  of  osteo- 
blasts  have  a  course  horizontal  to  the  bone  ;  but  in  the 
short  bones,  or  in  the  neighborhood  of  attachments,  this 
is  changed  to  a  direction  more  inclined  towards  the  coarse 
fibrous  layer,  and  the  particular  band  or  group  we  attempt 
to  follow  will  become  intermingled  with  others  and  lost. 
•At  another  point  immediately  adjacent,  the  fibers  are 
seen  cut  across  either  directly  or  diagonally ;  but  even 
among  these  will  be  seen  those  that  are  horizontal  to  the 
plane  of  the  section.  While  there  seems  to  be  no  uni- 
formity in  the  direction  of  the  fibers,  the  fibrous  appear- 
ance is  maintained,  giving  the  impression  of  an  intimate 
intermingling  rather  than  of  a  network.  This  appearance 
may  be  much  modified  by  the  manner  in  which  the  sec- 
tion is  prepared  for  observation.  If  it  be  with  a  good 
selective  stain  this  layer  in  young  animals  may  appear 
distinctly  cellular,  the  fibers  being  much  hidden,  while 
the  cells  are  made  prominent.  If  on  the  other  hand  the 
fibers  be  rendered  prominent  by  diffusive  carmine  stain- 
ing, osmic  acid,  or  pigmenting,  the  tissue  will  give  the 
impression  that  it  is  almost  wholly  fibrous.  The  various 
plans  of  preparation  should  be  employed  in  its  study. 
The  fibers  do  not  seem  to  branch  and  anastomose  as  in  a 
net,  but  rather  to  decussate  with  the  utmost  freedom, 
rarely  forming  groups  or  bands  of  any  considerable  num- 
ber running  in  a  common  direction.  However,  it  is 


THE   PERIOSTEUM.  31 

apparent  that  in  the  portion  next  to  the  layer  of  osteo- 
blasts  they  are  more  inclined  to  a  direction  horizontal  to 
the  surface  of  the  bone ;  while  in  the  portions  next  to 
the  coarse  fibrous  layer  their  general  direction  has 
become  perpendicular,  or  more  or  less  inclined  to  the  sur- 
face of  the  bone. 

In  the  long  bones  the  fibers  of  this  layer  in  the  non- 
attached  regions  very  generally  lie  horizontal  to  the  sur- 
face of  the  bone  throughout  its  thickness,  as  is  shown  in 
figs.  IT  and  18,  and  run  in  the  direction  of  its  long  axis. 
The  tissue  is  loose  in  texture  and  somewhat  embryonal 
in  its  character  immediately  adjacent  to  the  layer  of  osteo- 
blasts,  but  becomes  more  prominently  fibrous  as  the  bone 
is  receded  from.  Its  attachments  on  either  side  are  very 
loose  and  easily  broken  up  —  so  much  so  that  it  is  diffi- 
cult to  keep  the  parts  in  position  while  mounting  the 
sections.  In  those  sections  in  which  the  relations  of  the 
parts  are  a  little  disturbed  by  spreading  apart,  we  often 
obtain  the  best  displays  of  the  tissue  elements,  and  it  can 
be  seen  that  the  osteoblasts  have  processes  which  pass  in 
among  the  fibers  lying  next  to  them,  and  also  into  the 
bone,  forming  a  sort  of  attachment  to  it,  which  is,  how- 
ever, very  easily  broken  up.  This  is  well  shown  in  figs. 
17  and  18.  This  latter  form  is  common  to  the  shafts  of 
the  long  bones,  and  is  almost  universally  present  in  the 
non-attached  regions,  which  may  in  general  be  expected, 
except  in  the  region  of  the  attachments  of  muscles,  fasciae, 
ligaments,  or  the  approach  to  the  ends  of  the  bones. 
-  In  such  positions  the  form  of  the  attached  periosteum  is 
assumed. 

In  the  attached  portions  of  the  periosteum  the  fibers  of 
the  internal  layer  exhibit  a  definite  arrangement.  This 
presents  certain  variations  at  different  points,  but  these 
are  only  modifications  of  a  definite  plan.  Here  the  fibers 
are  not  separated  from  the  bone  by  the  layer  of  the  osteo- 
blasts, but  spring  directly  out  of  the  bone  itself,  and  the 


32  THE  PERIOSTEUM. 

osteoblasts  are  seen  to  be  disposed  between  the  fibers,  as 
in  figs.  20,  21,  23  and  24.  Perhaps  a  more  correct  state- 
ment would  be  that  the  fibers  spring  out  of  the  bone 
between  the  osteoblasts. 

At  some  points  the  former  statement  would  be  the 
more  correct,  for  the  reason  that  the  fibers  occupy  the 
greater  amount  of  territory,  so  that  the  osteoblasts  are 
crowded  into  various  forms  to  accommodate  them.  Every 
grade,  from  an  occasional  fiber  passing  out  of  the  bone 
between  the  osteoblasts,  to  an  increase  in  numbers  and 
size  which  represents  the  insertion  of  the  tendon,  in  which 
no  osteoblasts  are  present  between  the  fibers  may  be  found. 

In  the  attached  portions  then,  the  fibers  of  the  inner 
layer  of  the  periosteum  spring  directly  out  of  the  bone. 
In  order  that  this  may  be  well  seen  it  is  absolutely  neces- 
sary that  extremely  thin  sections  be  cut  parallel  with  the 
fibers  as  they  emerge  from  the  bone,  and  in  general  this 
will  also  give  a  good  view  of  the  arrangement  of  the 
fibers  of  this  layer  of  the  periosteum,  for  the  fibers  pur- 
sue the  same  general  course  until  they  reach  the  inner 
surface  of  the  coarse  fibrous  layer.  Each  of  these  fibers, 
after  passing  out  of  the  bone,  or  immediately  after  rising 
above  the  osteoblasts  between  them,  breaks  up  into  a 
tuft  of  very  fine  fibers  ;  indeed,  in  many  sections  it  is 
shown  that  that  which  in  the  main  appears  as  rather  a 
coarse  fiber  as  it  makes  its  exit  from  the  bone,  is  really  a 
compact  bundle  of  very  fine  ones.  These,  on  separating, 
spread  out  fan-like,  and  intermingling  and  decussating 
freely  with  others,  take  their  way  perpendicularly,  or 
inclined  somewhat  to  the  surface  of  the  bone,  to  the  inner 
surface  of  the  coarse  fibrous  layer  to  which  they  are 
attached.  The  arrangement  of  the  fibers  as  they  pass 
from  the  bone  to  the  coarse  fibrous  layer  varies  greatly  in 
different  positions.  The  most  common  form  seen  is  that 
in  which  all  of  them  pass  at  more  or  less  inclination  to 
the  perpendicular,  and  join  the  coarse  fibrous  layer  at  an 


THE    PERIOSTEUM.  33 

acute  angle,  as  shown  in  fig.  21.  Yet  every  angle  from 
about  45  to  90  degrees  may  be  met  with.  Occasionally, 
however,  we  see  them  joining  the  coarse  layer  in  inverse 
directions,  decussating  with  others  as  shown  in  fig.  20. 
It  is  quite  rare  that  the  fibers  join  the  coarse  layer  at 
right  angles.  In  many  instances  their  decussation  in  this 
layer  is  much  more  limited,  and  they  pass  quite  directly 
from  the  bone  to  the  coarse  layer,  forming  a  very  regular 
sheet  of  fibers  that  are  almost  parallel.  This  layer  has  no 
elastic  fibers,  or  at  least  they  must  be  rare.  Some 
observers  state  that  these  are  found  here,  but  I  have 
repeatedly  made  the  examination  in  the  manner  detailed 
below,  without  finding  them. 

ELASTIC    FIBERS. 

Elastic  fibers  form  a  network  in  the  coarse  fibrous  layer 
that  is  very  difficult  to  see  without  special  preparation. 
This  is  partly  on  account  of  the  fineness  of  the  fibers 
themselves,  but  more  especially  owing  to  their  relations 
to  the  coarse  ones.  In  fine  sections  stained  diffusely  with 
carmine  they  may  be  imperfectly  seen  as  white  lines,  but 
they  are  studied  to  best  advantage  by  dissolving  out  the 
white  fibers  on  the  stage  of  the  microscope.  If  this  is 
done  with  sufficient  care  their  arrangement  can  be  quite 
accurately  made  out.  This  is  done  as  follows  :  Place 
the  section  on  the  slide  in  water,  lay  on  a  cover  glass,  and 
carefully  dry  the  slide  at  its  edges  ;  now  fasten  the  cover 
securely  at  two  points,  preferably  next  the  edges  of  the 
slide,  with  a  little  gutta-percha  dissolved  in  chloroform, 
with  balsam,  or  with  wax.  Now  having  placed  the  slide 
on  the  stage  of  the  microscope  in  such  a  position  that  it 
will  be  inclined  from  end  to  end  (it  may  lie  flat  if  pre- 
ferred), lay  on  a  piece  of  blotting  paper  cut  to  fit  the 
circle  of  the  cover  glass  (a  square  cover  glass  may  be 
used),  and  lay  it  on  the  highest  end  of  the  slide  in  such 
a  position  that  it  will  touch  all  of  the  higher  edge  of  the 
5 


34  THE   PERIOSTEUM. 

cover  glass  not  covered  by  the  gutta  percha.  Also  lay  a 
piece  of  blotting  paper  on  the  opposite  end  of  the  slide, 
so  that  it  will  touch  the  margin  of  the  cover  glass.  Here 
a  central  point  of  contact  is  sufficient.  Thus  prepared, 
saturate  the  upper  bit  of  blotting  paper  with  a  strong 
solution  of  caustic  potash  (33  per  cent,  is  best).  This  will 
gradually  pass  through  under  the  cover  and  be  absorbed 
by  the  paper  below.  A  fresh  drop  should  be  added  every 
few  minutes  continuously  for  several  hours.  The  white 
fibers  will  first  swell  and  become  more  transparent,  and 
the  elastic  fibers  meantime  will  come  into  view.  Finally 
all  of  the  white  fibrous  tissue  will  slowly  melt  down  and 
disappear,  and  the  only  tissue  left  on  the  slide  will  be  the 
elastic  fibers  and  some  remains  of  the  bone. 

This  process  may  be  checked  at  any  stage  by  substi- 
tuting distilled  water  for  the  potash  solution,  and  if  this 
is  followed  by  glycerine,  and  glycerine  jelly,  a  permanent 
mount  of  the  object  can  be  effected.  It  must  be  borne 
in  mind  that  the  solution  of  the  tissue  can  not  be  stopped 
at  once,  and  the  particular  stage  desired  for  the  prepara- 
tion must  be  anticipated.  The  washing  with  distilled 
water  must  be  continued  for  a  considerable  time  to  remove 
all  of  the  potash. 

If  the  process  of  the  solution  of  the  tissue  be  closely 
watched  it  will  readily  be  discovered  that  the  elastic 
fibers  form  a  network  in  which  the  coarse  fibers  of  the 
periosteum  are  inclosed,  or  that  the  elastic  fibers  are  en- 
twined about  the  white  in  such  a  manner  as  to  prevent 
their  separation,  or,  if  they  are  somewhat  separated  by  a 
strain,  will  bring  them  back  by  their  elasticity.  I  have 
illustrated  such  a  network  in  fig.  22,  taken  from  a  section 
from  the  lower  jaw  of  the  same  series  as  that  represented 
in  fig.  21.  They  are  not  uniformly  distributed  in  the 
coarse  fibrous  layer,  but  seem  to  be  most  plentiful  where 
muscles  are  attached  to  a  rather  thick  outer  layer,  and 
the  regions  of  the  attachment  of  the  mucous  membranes. 


THE   PERIOSTEUM.  35 

Along  the  shafts  of  the  long  bones  I  have  usually  found 
very  few,  and  these  seem  not  to  penetrate  the  periosteum 
deeply  but  are,  indeed,  unusually  joined  to  its  surface, 
and  serve  to  make  a  very  loose  attachment  of  the  super- 
imposed tissue. 

The  inner  layer  of  fine  fibrous  tissue  of  the  periosteum 
is  generally  destitute  of  elastic  fibers.  Only  once  have  I 
seen  a  few  of  these  penetrating  to  the  surface  of  the  bone. 
Frequently  I  have  seen  a  few  fibers  passing  some  distance 
into  this  layer,  but  generally  they  are  confined  to  its  outer 
margin. 

The  blood-vessels  of  the  periosteum  are  quite  numerous, 
and  present  considerable  variations  in  different  regions. 
On  the  shafts  of  the  long  bones  the  larger  vessels  usually 
run  in  a  direction  parallel  to  the  long  axis  of  the  bone, 
and  lie  between  the  periosteum  and  the  superimposed 
tissues,  or  on  the  surface  of  the  periosteum.  These  branch 
laterally,  and  anastomose  in  such  a  manner  as  to  form  a 
tolerably  continuous  network.  This  network  receives 
here  and  there  branches  from  the  superimposed  tissues. 
In  some  situations,  especially  in  the  attached  portions, 
tfyis  network  lies  immediately  beneath  the  coarse  fibrous 
layer,  or  in  the  outer  part  of  the  internal  layer,  in  many 
instances  as  nearly  between  them  as  is  possible.  (Fig. 
21  D.)  However,  in  those  situations  in  which  the  coarse 
fibrous  layer  is  thickened  by  the  formation  of  two  or  more 
lamellae,  the  network  of  blood-vessels  is  often  found  be- 
tween these,  a  circumstance  which  has  given  rise  to  the 
statement  by  various  authorities  that  the  blood-vessels  of 
the  periosteum  are  found  mostly  in  the  outer  layer.  In 
my  observation  there  has  been  much  more  irregularity  in 
the  blood-vessels  of  the  periosteum  of  the  short  bones, 
which,  I  may  say,  would  naturally  be  expected,  both  as 
to  the  position  of  the  individual  layers,  and  the  regularity 
of  the  network  formed.  From  the  network  of  vessels 
thus  formed  in  any  of  these  positions  frequent  capillary 


36  THE   PERIOSTEUM. 

branches  are  given  off,  also  occasional  larger  vessels, 
which  pass  down  through  the  fibers  of  the  internal  coat 
and  enter  the  Haversian  canals  of  the  bone.  In  the  at- 
tached forms  of  this  coat,  these  branches  very  generally 
follow  the  direction  of  the  main  trend  of  the  fibers  of 
this  portion  of  the  periosteum,  and  in  a  few  localities  they 
are  quite  numerous,  especially  about  the  bones  of  the  face, 
and  notably  over  the  surfaces  of  the  alveolar  processes. 
In  the  portions  of  the  periosteum,  with  which  the  fibers 
of  the  mucous  membranes,  or  the  skin,  are  intimately 
blended,  the  position  of  the  blood-vessels  is  notably 
irregular ;  indeed,  they  seem  to  pertain  rather  to  the  super- 
imposed tissue  than  to  the  periosteum,  and  send  frequent 
branches  through  the  latter  to  the  Haversian  canals  of  the 
bone. 

Occasionally  I  have  noted  a  plexus  of  vessels  in  the  in- 
ternal layer  very  close  to  the  layer  of  osteoblasts,  but 
these  are  very  small  and  infrequent. 

The  nerves  of  the  periosteum  are  generally  few  in  num- 
ber ;  however,  a  considerable  number  of  the  larger  ves- 
sels are  accompanied  by  a  small  bundle  of  nerves,  which 
are  probably  distributed  mostly  to  the  blood-vessels  them- 
selves. They  enter  the  bones  with  most  of  the  larger 
branches  of  the  blood-vessels.  At  some  points,  nerves 
passing  through  the  periosteum  to  enter  the  canals  of  the 
bone  are  very  frequent.  These  are  points  where  the 
nerves  are  required  by  organs  situated  within  the  bone. 
The  supply  of  the  peridental  membranes  renders  them 
frequent  in  the  periosteum  of  the  alveolar  processes. 


CHAPTER  V. 

THE  CELLS  OF  THE  PERIOSTEUM. 

The  cellular  elements  of  the  periosteum  consist  of  de- 
veloping connective  tissue  cells  destined  to  form  osteo- 
blasts,  osteoclasts  and  fibroblasts.  The  fibroblasts  are 
such  as  are  destined  to  reconstruct  or  augment  in  num- 
bers the  fibers  of  this  membrane  and  have  been  suffi- 
ciently considered.  However,  I  may  say  that  a  consider- 
able number  of  connective  tissue  cells  are  found  that  seem 
not  to  show  specific  character.  They  seem  not  to  be  pro- 
ceeding regularly  to  the  development  of  fibrous  material 
nor  to  be  allying  themselves  to  either  of  the  other  two 
forms,  and  are  probably  cells  that  have  missed  their  des- 
tiny and  therefore  have  developed,  irregularly.  By  care- 
ful search  a  variety  of  such  may  be  found.  They  are 
mostly  round  or  oval  nucleated  forms,  but  occasionally 
irregular  star-shaped  forms  present  themselves.  Such 
cells  seem  to  have  no  function  to  perform  in  connection 
with  this  membrane  or  in  the  locality  in  which  they  are 
found  ;  they  are  not  sufficiently  numerous  and  regular  in 
their  distribution  for  me  to  suppose  that  they  perform 
some  undiscovered  function  which  renders  their  presence 
necessary.  Hence  the  supposition  that  they  are  cells 
which  have  missed  their  destiny  and  finally  disintegrate 
and  disappear.  In  the  progress  of  our  study  of  the  other 
cell-forms,  the  function  of  which  is  obvious,  we  shall  find 
sufficient  evidence  of  faulty  action,  or  of  over-activity  in 
certain  directions,  which  is  yet  within  the  range  of  what 
may  be  termed  physiological  errors  on  the  part  of  the 
elementary  forms.  These  are  errors  in  direction  of 
growth,  or  removal  of  tissues,  which  are  checked  before 

37 


38  THE   CELLS   OF  THE  PERIOSTEUM. 

they  become  so  pronounced  as  to  be  regarded  as  patho- 
logical; as,  for  instance,  in  the  case  of  absorption  of  bone 
beyond  the  needs  of  the  time  and  its  reconstruction  after- 
ward. By  English  writers  the  osteoblasts  are  usually 
reckoned  as  belonging  to  the  periosteum,  while  some  of 
the  German  authors  have  classed  them  as  belonging  to 
the  bones,  and  designated  them  as  the  cambium  layer. 
So  far  as  they  are  connected  with  the  periosteum  at  all, 
their  place  is  between  the  periosteum  and  bone  in  the 
non-attached  forms,  and  upon  the  bone  between  the  pene- 
trating fibers  in  the  attached  forms.  However,  the  num- 
ber of  embryonal  cells  that  are  found  among  the  fibers  of 
the  periosteum  in  the  immediate  vicinity  of  the  bone, 
gives  the  impression  that  this  portion  of  the  tissue  is  the 
place  of  the  development  of  the  osteoblasts,  and  that  these 
cells  are  destined  to  become  such.  The  most  plausible 
supposition  is  that  these  embryonal  cells  are  leucocytes 
that  have  wandered  in  here  from  the  blood  streams,  not 
by  any  manner  of  chance,  as  this  expression  might  indi- 
cate, but  through  the  control  of  some  unseen  power  which 
causes  these  cells  to  congregate  where  they  are  needed 
for  building  up  of  new  tissues,  or  the  repair  of  injuries  to 
the  old ;  and  to  develop  into  the  necessary  forms  for  this 
purpose,  whether  it  be  for  the  formation  of  fibrous  tissues, 
the  formation  of  bone,  the  absorption  of  bone,  or  for 
whatever  else  may  be  needed  which  is  in  the  power  of  the 
connective  tissue  cell  to  perform. 

The  osteoblasts  are  polygonal  cells  which  lie  upon  the 
surface  of  the  bone  and  usually  clothe  it  as  epithelium 
clothes  the  mucous  membranes.  They  vary  greatly  in 
size,  so  much  so,  indeed,  that  no  measurement  will  give 
a  very  accurate  idea  of  them.  They  are  also  placed  very 
differently  in  relation  to  the  bone  in  different  positions 
and  under  varying  conditions.  In  case  of  young  bones 
that  are  rapidly  growing  they  are  often  very  much  crowded 
together,  and  thus  compressed  into  a  great  variety  of 


THE   CELLS   OF  THE  PERIOSTEUM.  39 

forms.  Occasionally  they  are  very  much  elongated,  as, 
for  instance  some  of  the  cells  in  fig.  25,  taken  from  a  cross 
section  of  the  tibia  of  a  young  kitten.  Here  it  will  be 
seen  that  some  of  the  cells  reach  the  bone  only  by  ex- 
tending a  process-like  elongation  between  the  neighboring 
cells  (a)  while  others  seem  to  be  flattening  down  upon  the 
surface  (b).  In  my  studies  it  has  seemed  to  me  that  only 
those  cells  which  are  attached  to  the  bone  should  be  con- 
sidered as  osteoblasts.  They  are  undoubtedly  developed 
from  the  embryonal  cells  of  the  neighborhood,  but  it  is 
not  until  the  time  of  their  attachment  to  the  bone  that 
their  destiny  can  be  definitely  determined.  Therefore, 
we  can  hardly  say  that  more  than  a  single  layer  of  these 
cells  is  ever  found  upon  the  bone  in  any  case.  More  than 
one  layer  is  often  made  to  appear  by  cutting  sections 
diagonal  to  the  surface  of  the  bone. 

The  more  usual  forms  of  the  osteoblasts  appear  in  figs. 
17  and  18,  where  there  are  not  too  many  to  conveniently 
cover  the  surface  ;  and  by  the  slight  shrinkage  that  is 
almost  inevitable  in  histological  preparations,  they  are 
made  to  stand  slightly  apart.  The  processes  of  these  cells 
appear  prominently  in  figs.  17  and  18.  These  are  very 
difficult  of  observation,  and  it  is  only  under  especially 
favorable  circumstances  that  they  appear ;  however,  they 
are  seen  so  frequently  in  favorable  positions  as  to  lead  to 
the  supposition  that  all  osteoblasts  that  are  so  far  devel- 
oped as  to  come  to  lie  upon  the  bone  possess  them. 

These  cells  are  found  also  lining  the  Haversian  canals, 
and  the  interior  of  the  hollow  bones  at  all  points  that 
present  augmentation  by  growth.  They  are  therefore  not 
peculiar  to  the  periosteum.  In  the  case  of  old  persons 
and  animals,  when  the  growth  of  the  bones  has  ceased, 
the  osteoblasts  are  lessened  in  numbers,  and  have  changed 
their  forms  in  such  manner  as  to  lie  upon  the  surface  of 
the  bone  as  thin  flattened  scales,  which  often  can  not  be 
seen  upon  the  margin  in  sections  cut  perpendicular  to  the 


40          THE  CELLS  OP  THE  PERIOSTEUM. 

surface ;  but  in  such  sections  they  will  appear  whenever 
a  Haversian  canal  is  so  cut  as  to  present  the  flat  sides  of 
the  cells  to  view,  especially  if  stained  with  a  good  nucleus 
tinting  dye.  In  this  condition  the  cells  seem  to  be  inac- 
tive. In  the  study  of  young  bones  many  regions  of  in- 
activity may  be  met  with  in  which  the  osteoblasts  present 
this  appearance. 

The  function  of  the  osteoblasts  is  clearly  the  formation 
of  bone.  There  is  no  growth  of  bone  without  their  pres- 
ence. It  is  true  that  calcifications  of  tissue  occur  in 
various  places  without  the  presence  of  osteoblasts,  and  to 
the  naked  eye  these  may  closely  resemble  bone ;  but  upon 
microscopic  examination  they  are  found  not  to  present  the 
tissue  forms  of  bone.  These  tissue  forms  are  directly  the 
product  of  the  osteoblasts.  The  precise  manner  of  the 
formation  of  bone  is  not  agreed  upon,  two  theories  still 
being  entertained.  These  may  be  briefly  stated.  The 
one  view  regards  the  osteoblasts  as  forming  the  matrix  by 
aggregating  themselves  together  upon  the  surface  of  the 
bone.  This  matrix  thus  formed  is  in  turn  converted  into 
bone  by  becoming  infiltrated  with  lime  salts.  All  bone 
is  shown  by  certain  processes  of  chemical  solution,  to  be 
composed  of  delicate  laminae  laid  the  one  upon  the  other 
horizontal  to  the  growing  surface,  whether  this  be  the 
surface  of  the  bone  proper,  or  the  surface  of  the  Haver- 
sian canals.  It  is  supposed,  according  to  this  view,  that 
these  laminae  are  made  up  from  the  different  layers  of 
consolidated  osteoblasts.  In  this  process  certain  of  the 
osteoblasts  persist,  or  are  included  in  the  formed  bone 
without  calcification,  and  thus  become  the  bone  cor- 
puscles. 

There  are  many  objections  to  this  view.  One  of  the 
most  potent  is  the  fact  that  the  osteoblastic  layer  is  very 
rarely  found  in  a  condition  of  even  semi-consolidation. 
The  cells  do  not  approach  the  loss  of  individuality  neces- 
sary to  the  formation  of  a  continuous  sheet  of  matrix. 


THE  CELLS   OP  THE   PERIOSTEUM.  41 

In  reasonably  good  preparations  they  always  appear  as 
individualized  cells.  Furthermore,  we  are  not  able  by 
any  treatment  of  bone  yet  devised,  to  render  the  outlines 
of  such  cellular  elements  of  its  matrix  apparent.  These 
objections  to  this  view  has  been  pointed  out  by  a  number 
of  prominent  histologists. 

Another  view  is  that  the  osteoblasts  shed  out  from 
themselves  the  material  that  forms  the  bone  by  some  pro- 
cess closely  akin  to  secretion,  if  it  be  not  this  in  fact. 
It  seems  probable  that  this  process  of  secretion  is  per- 
formed by  all  of  these  cells  that  lie  against  the  bone,  and 
that  the  process  is  not  continuous,  but  presents  alterna- 
tions of  activity  and  rest.  This  will  account  for  the 
lamellation  observed  in  bone  more  perfectly  perhaps,  than 
the  supposition  previously  mentioned.  This  kind  of  lamel- 
lation is  also  observed  in  the  structure  of  the  shells  of 
shellfish,  the  formation  of  which  is  generally  agreed  to 
be  by  a  process  of  secretion.  In  the  formation  of  bone  by 
this  process,  certain  cells  seem  to  become  matured  and 
flattened  down  against  the  surface,  and  to  sink  beneath 
it.  As  a  matter  of  fact,  the  bone  material  is  built  up 
over  them  and  they  become  encapsuled,  and  are  then 
known  as  bone  corpuscles.  They  lose  bulk  in  this  pro- 
cess, so  that  the  bone  corpuscle  is  usually  smaller  than 
the  original  osteoblast.  It  is  difficult  to  see  the  processes 
of  the  bone  corpuscles  in  moist  specimens,  but  they  are 
plainly  apparent  in  sections  of  dried  bone,  in  which  the 
canaliculi,  which  were  occupied  by  them,  are  filled  with 
air.  The  cells  that  sink  into  the  bone  in  this  manner, 
while  not  entirely  regular  in  number  and  distance  from 
each  other,  do  present  a  kind  of  regularity  which  serves 
to  give  the  impression  of  rows  around  the  Haversian 
canals,  and  along  the  borders  of  sub-periosteal  bone  (in 
cross  sections  of  the  long  bones).  These  rows  bear  a 
pretty  distinct  relation  to  the  lamellae  of  the  bone,  as 
would  naturally  be  expected  if  either  of  these  explana- 
6 


42  THE   CELLS    OF   THE   PERIOSTEUM. 

tions  of  the  process  be  adopted.  The  osteoblasts  in 
flattening  down  very  generally  lie  lengthwise  upon  the 
long  bones,  therefore  the  resulting  bone  corpuscle  lies  in 
the  same  manner  with  its  broadest  diameter  to  the  form- 
ing surface,  whether  this  surface  be  that  of  the  wall  of  a 
Haversian  canal,  or  the  surface  of  the  bone.  Therefore, 
in  cross  sections  of  the  long  bones  we  get  cross  sections 
of  these  cells,  so  that  they  present  a  somewhat  different 
appearance  from  that  seen  in  the  lengthwise  sections. 

The  processes  of  the  bone  corpuscles  are  very  numer- 
ous, and  radiate  in  every  direction  through  the  bone 
matrix  forming  junctions  with  each  other.  (See  fig.  25  c.) 
Each  individual  bone  corpuscle  with  its  processes  seems 
to  preside  over  a  specific  area  of  bone  matrix,  and  the 
impression  might  be  entertained  that  this  individual 
corpuscle  had  formed  this  area.  This  impression  is  also 
much  strengthened  when  in  the  study  of  irregular  for- 
mations, globules  of  bone  are  found,  each  showing  a  single 
bone  corpuscle  near  its  center;  or  perhaps  several  of 
these  lying  together  with  the  area  of  each  more  or  less 
clearly  visible.  In  studying  these,  it  is  often  difficult  to 
escape  the  conviction  that  each  osteoblast  that  so  matures 
as  to  become  a  bone  corpuscle  really  forms  the  area  of 
bone  with  which  it  is  immediately  surrounded.  How- 
ever, the  study  of  the  forming  surface  will  serve  to  dispel 
this  idea  and  admit  the  assistance  of  osteoblasts  not  yet 
so  fully  matured.  Again,  a  close  study  of  the  processes 
of  the  bone  corpuscles  shows  that  their  general  direction 
is  perpendicular  to  the  forming  surface  of  the  bone  (fig. 
25),  so  much  so  that  with  low  powers  a  striation  in  this 
direction  often  becomes  prominent.  Much  of  this  is  due 
to  the  processes  reaching  far  into  the  bone  before  the 
encapsuling  occurs. 

In  those  portions  of  bone  formed  under  an  attached 
periosteum,  particularly  if  the  penetrating  fibers  are 
numerous  and  large  as  shown  in  figs.  20,  21,  23  and  24  the 


THE  CELLS   OF   THE   PERIOSTEUM.  43 

bone  corpuscles  do  not  lie  with  their  long  axes  horizontal 
to  the  surface  of  the  bone,  but  in  a  line  parallel  with  the 
penetrating  or  residual  fibers.  This  is  explained  by  the 
fact  that  the  osteoblasts  are  held,  or  lie  between  the 
fibers  in  such  a  way  as  to  present  their  short  diameters  or 
ends  to  the  surface  of  the  bone,  which  position  they 
retain.  It  serves  as  a  mark  designating  the  portions  of 
the  bone  formed  under  a  periosteum  of  this  character 
even  when  the  fibers  themselves  can  not  be  seen.  This 
applies  to  all  those  forms  of  the  attached  periosteum  in 
which  the  penetrating  fibers  are  large  and  thickly  set. 
When  the  fibers  are  more  sparsely  distributed  the  osteo- 
blasts and  the  resulting  bone  corpuscles,  may  lie  in  the 
same  relative  position  to  the  forming  surface,  as  in  case  of 
the  non-attached  forms. 

The  osteoclasts,  myoplaxes  or  giant-cells,  present 
various  forms,  vary  indefinitely  in  size,  and  are  usually 
multinucleated.  (See  figs.  19  /,  /,  /,  24  g  and  27,  a,  a.) 
Occasionally,  one  may  be  recognized  with  but  a  single 
nucleus,  and  I  have  seen  them  containing  as  many  as 
twenty-four.  From  four  to  ten  is  a  more  common  num- 
ber. The  general  inclination  is  to  the  round  or  oblojig 
form.  They  are  very  rarely  branched  and  present  no 
processes.  Such  forms  of  cell  may  be  found  in  other 
localities,  and  we  can  only  recognize  them  definitely  as 
osteoclasts,  when  found  in  contact  with  bone,  or  some  of 
the  hard  tissues  undergoing  absorption.  In  such  posi- 
tions, they  uniformly  lie  in  little  bay-like  excavations  in 
the  surface,  known  as  the  lacunae  of  Howship.  They 
conform  in  certain  measure  to  the  depth  and  size  of  the 
excavation  in  which  they  lie,  which  fact  seems  to  argue 
that  most  of  their  growth  has  occurred  in  this  position.  I 
often  see  very  small  ones  in  small  excavations  and  large 
ones  in  correspondingly  large  excavations.  But  in  ab- 
sorption of  greater  extent,  such  as  in  the  hollowing  out  of 
the  shafts  of  the  long  bones,  we  often  find  very  large  cells 


44  THE   CELLS   OF  THE   PERIOSTEUM. 

lying  on  the  surface  of  the  bone  without  any  lacunae  what- 
ever. I  may  say,  however,  that  the  number  of  such  cells 
that  are  sometimes  seen  in  the  tissues  of  the  bone  marrow, 
detached  from  the  bone,  but  in  the  neighborhood  of 
extensive  absorption,  has  given  me  the  impression  that 
possibly  these  cells  may  in  some  degree  possess  amreboid 
movement  during  life,  and  therefore,  a  limited  power  of 
migration. 

The  function  of  these  cells  is  sufficiently  obvious. 
They  dissolve  the  bone  with  which  they  are  in  contact, 
probably  by  the  secretion  of  a  solvent  fluid,  making  room 
for  themselves,  and  in  this  way  remove  the  surface  of  the 
bone,  i.  e.,  cause  its  absorption.  In  this  way  the  en- 
larged ends  of  the  bone  are  trimmed  down  to  the  size  of 
the  shaft  (in  the  elongation  of  the  bones  during  growth), 
and  the  central  cavities  are  hollowed  out.  Channels  are 
burrowed  through  and  new  bone  again  deposited,  thus  re- 
moving the  old  and  filling  in  with  new.  In  this  work  the 
osteoblasts  and  the  osteoclasts  are  continually  replacing 
each  other,  the  osteoblasts  building  and  the  osteoclasts 
tearing  down ;  and  by  the  joint  action  of  these,  both  the 
formation  and  the  conformation  of  the  bones  are  affected. 


CHAPTER  VI. 

FORMATION   OF  BONE. 

Histologists  have  usually  described  three  modes  of 
the  formation  of  bone.  These  relate  to  the  conditions 
under  which  the  bone  is  formed,  and  are  the  subperiosteal, 
intra-cartilaginous  and  intra-membranous.  The  subperi- 
osteal is  not  a  de  novo  origin,  but  a  growth  superadded  to 
previously  formed  bone,  or  laid  down  upon  the  surface  of 
cartilage.  This  has  been  in  a  measure  considered  while 
describing  the  functions  of  the  osteoblasts,  but  certain 
points  should  be  elucidated.  The  surface  of  a  growing 
bone  is  not  smooth  and  compact,  but  is  continually  thrown 
into  convolutions  by  the  upward  growth  of  spiculse,  or 
upon  long  bones,  of  long  ridges  more  or  less  sharp, 
arranged  parallel  with  the  long  axis  and  which  often  ris- 
ing into  the  tissues  of  the  periosteum,  form  arches  by 
spreading  laterally  and  joining  with  like  ridges  on  either 
side,  as  shown  in  figs.  23  a,  a,  and  26  c,  <?,  <?,  both  of  which 
are  from  sections  cut  across  the  long  axis  of  the  formation. 
In  this  manner  new  Haversian  canals  are  being  formed 
into  which  capillary  vessels  are  sent  to  supply  the  parts 
with  blood.  By  this  means  the  extent  of  surface  to  which 
the  osteoblasts  are  applied  for  the  building  of  bone  is 
immensely  augmented.  As  one  set  of  Haversian  canals 
is  completed  in  this  manner,  indeed  often  before  their 
completion,  new  spiculae,  or  ridges  of  bone,  are  again  pro- 
jected from  the  surface  to  form  others  exterior  to  these. 
The  Haversian  canals  thus  formed  are  already  lined  with 
osteoblasts,  which  continue  the  work  of  deposit  of  bone 
upon  their  walls,  and  thus  the  bone  grows  not  only  upon 
its  surface,  but  on  the  walls  of  the  canals  also.  This 

45 


46  FORMATION   OF   BONE. 

is  best  seen  in  fig.  26,  in  which  a  comparatively  low  power 
is  used  for  the  illustration  of  a  portion  of  a  cross  section 
from  the  tibia  of  the  kitten.  At  <?,  c,  are  shown  upward 
growths  of  spiculae,  into  the  tissue  of  the  inner  layer  of 
the  periosteum.  At  c?,  these  are  throwing  out  processes 
from  their  summits.  At  e,  these  are  just  meeting  to- 
gether, and  at/,  fully  formed  canals  are  seen.  It  will  be 
noted  that  the  bone  is  thickly  studded  with  them. 

The  soft  tissue  as  it  is  included  in  these  Haversian 
canals  changes  its  type  very  noticeably,  losing  most  of  its 
fibers,  and  becoming  still  more  like  fetal  tissue,  presenting 
many  undeveloped  cells  which  in  the  main  lie  quite  widely 
apart,  giving  a  tissue  of  very  simple  character. 

As  has  been  indicated,  the  subperiosteal  bone  is 
deposited  in  laminae  that  are  concentric  to  the  axis  of  the 
shaft  of  the  bone,  and  the  position  of  the  bone  corpuscles 
corresponds  with  these,  presenting  their  flattened  sides 
to  the  surface,  and  therefore  in  the  absence  of  these  con- 
volutions of  the  surface,  present  laminae  arranged  around 
the  shaft.  But  in  this  convolution  of  the  surface,  the 
arrangement  of  these  laminae,  and  also  the  position  of  the 
bone  corpuscles  is  in  accord  with  the  surface  at  the  time 
of  its  formation.  It  will  be  seen  that  this  produces  a 
seeming  confusion  in  the  laminae  and  position  of  the 
corpuscles  in  th*e  portions  of  bone  thus  formed.  The 
bone  formed  on  the  walls  of  a  Haversian  canal  presents 
concentric  rings  around  the  axis  of  the  canal  to  which  the 
bone  corpuscles  also  present  their  flattened  sides,  thus  dis- 
tinguishing this  bone  from  the  subperiosteal  formation. 
These  rings  of  Haversian  bone  are  known  as  Haversian 
systems,  and  they  play  a  very  important  part  in  the 
growth  of  bone. 

This  subperiosteal  formation  of  Haversian  canals  is  not 
confined  to  the  non-attached  forms  of  the  periosteum,  but 
occurs  beneath  the  attached  also,  though  less  regularly. 
It  seems  that  where  the  penetrating  fibers  are  very  large 


FORMATION   OF  BONE.  47 

and  numerous,  very  few  such  canals  are  formed.  In 
these  the  upward  growth  of  the  spiculse  is  generally  along 
the  line  of  some  of  the  fibers,  and  as  the  arches  are  thrown 
out  on  either  side,  the  fibers  of  the  region  are  included  in 
the  bony  formations  without  disturbing  their  position,  but 
that  portion  of  the  fibers  which  is  included  in  the  Haver- 
sian  canal  soon  disappears,  so  that  the  Haversian  bone  has 
very  few  or  none  of  these.  (Figs.  21  A,  A,  and  23  5,  5,  i,  6.) 
In  some  instances  in  which  the  fibers  are  unusually  large 
and  strong,  as  in  the  alveolar  process,  which  I  will  describe 
in  connection  with  the  peridental  membrane,  the  fibers  are 
often  seen  stretching  across  fully  formed  Haversian  canals, 
thus  showing  a  tendency  to  persist,  or  that  large  and 
strong  fibers  are  removed  more  slowly.  In  many  instan- 
ces, however,  especially  about  the  bones  of  the  face  where 
there  are  unusually  strong  periosteal  attachments,  the  sub- 
periosteal  growth  of  bone  is  originally  destitute  of  Haver- 
sian canals  and  thickly  set  with  penetrating,  or  residual 
fibers.  These  fibers  are  not  a  part  of  the  bone  per  se,  but 
are  the  accident  of  the  formation.  In  other  words,  the 
method  of  making  firm  hold  upon  the  bone,  is  the  implan- 
tation of  the  fibers  by  building  the  bone  about  them  ;  and 
after  enough  of  the  length  has  been  included  in  this  way 
to  serve  that  purpose,  the  deeper  portions  are  of  no  fur- 
ther use,  and  as  a  matter  of  fact,  are.  according  to  my 
own  observation,  removed. 

This  is  accomplished  by  the  removal,  not  of  the  fibers 
simply,  but  of  the  whole  mass  of  bone  thus  formed,  by  the 
successive  burrowing  of  Haversian  canals  through  its  sub- 
stance, and  the  formation  of  what  may  very  properly  be 
termed  secondary  Haversian  systems.  I  have  illustrated 
this  in  fig.  24  from  a  section  from  the  lower  jaw  under  a 
muscular  attachment.  Here  it  will  be  seen  that  the  pene- 
trating fibers  of  the  periosteum  are  strong  and  thickly  set, 
and  though  the  surface  of  the  bone  presents  some  low  spicu- 
Ise  reaching  out  along  the  line  of  some  of  the  fibers  it  is  really 


48  FORMATION  OP  BONE. 

a  solid  growth  of  subperiosteal  bone.  A  little  way  inward 
from  the  surface,  however,  there  is  a  Haversian  canal 
which  fortunately  presents  a  direct  lengthwise  section. 
On  the  walls  of  this  canal  from  the  letter  c  to  the  line 
drawn  across  at  e,  Haversian  bone  is  deposited,  and  the 
canal  itself  is  lined  with  osteoblasts.  Above  the  line  e, 
there  is  no  deposit  of  Haversian  bone,  and  instead  of 
osteoblasts,  the  walls  are  lined  with  osteoclasts,  which  lie 
in  little  bay  like  excavations,  g.  In  this  part  of  the  canal 
the  excavation  of  the  subperiosteal  bone  is  in  active  pro- 
gress, while  in  the  parts  below  the  line  e,  the  excavation 
is  being  filled  up  with  Haversian  bone.  This  is  readily 
distinguished  .  from  the  subperiosteal  bone  by  noticing 
three  points.  1st.  The  Haversian  bone  is  slightly  differ- 
ent in  shade  from  the  subperiosteal.  2d.  The  long  axis 
of  the  bone  corpuscles  lie  in  a  different  position,  or  in  the 
direction  of  the  long  axis  of  the  Haversian  canal.  3d.  It 
has  no  residual  fibers.  Now  if  we  scrutinize  the  original 
walls  of  the  canal  where  the  Haversian  bone  joins  the 
subpeiiosteal,  it  will  be  seen  that  they  are  everywhere 
indented  with  the  bay  like  excavations  as  pointed  out  at 
/,  /,  /.  These  may  be  contrasted  with  similar  Haversian 
growths,  shown  in  Haversian  canals  of  subperiosteal  for- 
mation, in  figs.  21  and  25,  which  do  not  show  these  bay 
like  forms.  Wherever  these  are  found  they  are  the 
marks  of  the  work  of  the  osteoclasts,  and  show  the  canals, 
or  Haversian  systems,  deposited  therein  to  be  secondary 
formations,  that  is  to  say,  formed  by  the  removal  of  previ- 
ously formed  bone.  In  my  studies  of  the  bones  of  the 
jaws  in  animals  of  different  ages,  1  find  that  almost  the 
entire  original  formation  of  bone  is  removed  in  this  way, 
and  replaced  by  Haversian  bone.  This  seems  to  be  espec- 
ially the  case  at  all  points  where  there  are  many  residual 
fibers,  so  that  in  old  bones  these  fibers  penetrate  to  but  a 
slight  depth,  otherwise  they  occur  only  at  isolated  spots 
that  have  been  missed  by  the  process  of  removal.  In  the 


FORMATION    OF   BONE.  49 

growth  of  the  long  bones,  where  the  residual  fibers  are 
localized  at  particular  points,  the  same  removal  seems  to 
occur.  In  the  regions  of  the  non-attached  periosteum 
this  kind  of  regeneration  may  also  be  found,  but  it  seems 
not  so  complete. 

These  residual  fibers  are  known  in  our  literature  as 
penetrating  fibers,  or  fibers  of  Sharpey,  who  tirst  described 
them  as  fibers  penetrating  the  laminse,  i.  e.,  passing  in 
a  direction  transverse  to  the  laminae  of  bone.  While  this 
observer  with  others  who  have  followed  him,  seems  to 
have  recognized  that  these  were  in  many  instances  de- 
rived from  the  periosteum,  and  were  irregular  in  their 
occurrence,  it  seems  that  the  fundamental  reason  for  their 
appearance  was  missed  by  them,  which  is  probably  to  be 
explained  by  the  fact  that  in  their  study  of  the  subject, 
the  varietjr  of  the  fibrous  forms  and  purposes  of  the  peri- 
osteum had  not  attracted  special  attention.  It  will  be 
clearly  seen  that  it  is  only  by  a  close  study  of  this  mem- 
brane in  different  positions,  giving  attention  to  the  pur- 
poses it  subserves,  and  the  forms  adapted  to  these,  that 
we  may  gain  a  clue  to  the  uses  of  these  fibers,  and  become 
able  to  know  in  advance  where  to  find  them  in  abundance 
and  thus  be  able  to  follow  up  the  study  of  them  satisfac- 
torily. These  localities  have  been  sufficiently  indicated. 

The  function  of  these  fibers,  it  seems  to  me,  is  physical 
and  entirely  passive ;  that  of  giving  firm  attachment  to 
the  periosteum  and  the  tissues -it  supports.  They  may 
give  direction  in  many  instances  to  the  growth  of  bone 
by  forming  a  kind  of  ladder,  or  central  line,  around  which 
osteoblasts  may  concentrate,  but  in  no  other  way  contrib- 
uting to  that  growth.  The  active  functioning  process  is 
to  be  sought  for  in  the  act  of  the  formation  of  the  fiber, 
not  in  the  fiber  after  its  formation,  and  I  see  no  reason  for 
considering  these  in  any  other  light  than  as  white  con- 
nective tissue  fibers,  subserving  a  specific  purpose,  that  of 
giving  support.  I  should,  therefore,  regard  the  term 
7 


50  FORMATION  OF  BONE. 

osteogenetic  fibers  consisting  of  osteogenetic  substance,  ap- 
plied to  them  by  Sharpey  and  adopted  by  many  histolo- 
gists,  as  an  error.     It  is  true,  as  pointed  out  by  the  above 
named  observer  and  others,  that  in  the  upward  growth  of 
spiculse  of  bone,  for  the  formation  of  Haversian  canals, 
the  line  of  these  fibers,  if  they  are  present  as. penetrating 
fibers,  is  followed,  and  that  the  osteoblasts  are  arranged 
about  them  and  seem  to  be  clinging  to  them.     It  is  also 
true,  that  we  find  these  osteoblasts  arranged  about  a  cen- 
ter  of  advance  of  bony  spiculse  in  the  absence  of  such 
fibers,  where  the  growth  is  taking  place  under  the  non- 
attached  forms  of  the  periosteum.     I  have  scrutinized  this 
point  closely,    employing  as   aids   the   various  plans   of 
preparation  and  staining,  without  being  able  to  make  out 
any  such  fiber  or  fibers,  that  would  seem  to  be  in  any  way 
directing  the  growth,  but  on  the  contrary,  have  found  the 
growth  of  such  spiculse  proceeding  across  the  line  of  the 
horizontal  fibers  of  the  non-attached  forms  of  the  perios- 
teum.    Again,  as  has  already  been  stated,  even  in  the  at- 
tached forms,  where  the  upward  growth  of  spiculse  follows 
the  line  of  particular  fibers,  the  processes  given  off  at 
either  side,  forming  the  arch  connecting  with  neighboring 
spiculse,   for   the   formation    of  Haversian   canals,    pass 
directly  across  the  direction  of  these  fibers  without  dis- 
turbance of  their  position.     These  facts  show  that  the 
formed  fibers  become  passive  physical  agents,  and  have 
not   a   genetic   function.     It   is   probable  that  in   many 
instances,  as  in  the  intra-membranous  formation  of  bone, 
which  will  be  studied  later,  the  formation  of  fibers  is  a 
necessary  step  in  advance,  affording  a  kind  of  framework 
or  lattice,  as  a  basis  for  the  new  growth,  but  in  every  in- 
stance, the  work  of  deposit  of  new  bone  is  performed  in 
the  presence  of,  and  by,  the  osteoblasts,  which  are  special- 
ized from  the  embryonic  connective  tissue  cells,  and  are  in 
no  way  dependent  upon  the  fibers,  except  as  these  afford 


FORMATION   OF  BONE.  51 

a  meshwork,  in  which  they  may  undergo  their  develop- 
mental stage.. 

The  condition  of  these  fibers  as  to  calcification  is  of 
interest,  although  not  very  positively  made  out.  In 
many  instances  they  appear  to  have  become  stiffened  by 
the  reception  of  lime  salts  in  advance  of  the  line  of  the 
forming  bone,  and  thus  become  a  nidus  for  the  upward 
growth  of  spiculse.  In  other  instances  appearances  indi- 
cate quite  the  reverse  condition,  and  in  some  very  thin 
sections  cut  across  the  fibers,  I  have  found  them  so  loosely 
attached  near  the  border  of  the  forming  bone,  that  they 
have  fallen  out  of  their  alveoli.  Occasionally  quite  deep 
in  the  substance  of  the  bone  I  have  found  them  protruding 
from  the  broken  margins  of  the  section,  as  illustrated  at 
<7,  #,  #,  in  fig.  21.  Furthermore,  in  pulling  apart  the  lam- 
inae of  subperiosteal  bone,  we  may  find  them  withdrawn 
to  some  length  as  has  been  so  admirably  illustrated  by 
Sharpey.  (Quain's  Anatomy.)  These  facts  show  the 
loose  connection  of  the  fibers  with  the  bone  substance, 
but  it  must  be  remembered  that  this  is  only  after  the  with- 
drawal of  the  lime  salts  by  the  process  of  decalcification 
in  the  preparation  of  the  tissue.  Before  the  decalcifica- 
tion, these  points  can  not  be  demonstrated.  It  therefore 
appears  that  the  connection  of  these  fibers  is  not  intimate 
with  the  basis  substance  of  the  bone,  but  that  they  are 
rendered  firm  and  seemingly  of  equal  consistence  with 
that  matrix,  by  the  common  reception  of  lime  salts,  in  the 
process  of  calcification. 

With  the  description  given  above,  and  the  illustrations 
presented,  it  will  become  clear  that  isolated  patches  of 
these  fibers  may  be  found  that  do  not  reach  the  surface  of 
the  bone,  having  been  cut  off  by  the  formation  of  Haver- 
sian  systems.  Again  the  fibers  may  be  cut  away  by 
absorptions  occurring  beneath  the  periosteum,  the  por- 
tions so  absorbed  being  refilled  with  bone,  and  the  sub- 
periosteal growth  proceeding  as  before.  I  have  been  so 


52  FORMATION   OF  BONE. 

fortunate  as  to  meet  with  examples  of  this  in  my  sections, 
one  of  which  is  presented  in  fig.  27.  This  fact  serves  also 
to  explain  some  things  which  heretofore  seemed  dark  in 
the  formation  of  the  cementum  on  the  roots  of  the  teeth, 
which  will  be  studied  later.  In  the  figure  it  will  be  seen 
that  at  a,  a,  there  are  several  osteoclasts  lying  in  deep 
excavations,  and  at  5,  5,  there  are  points  at  the  unabsorbed 
surface  of  the  bone  in  which  the  fibers  of  the  periosteum 
are  seen  implanted.  The  fibers  appear  also  deep  in  the 
bone,  and  it  will  be  seen  that  in  the  region  of  the  absorp- 
tion c,  c,  these  have  been  removed,  together  with  the 
bone,  and  the  space  filled  with  tissue  of  a  marked  fetal 
type,  but  containing  a  large  number  of  developing  cells. 
In  many  instances  I  have  seen  such  absorptions  that  have 
been  refilled  with  bone,  and  the  fibers  reattached  only 
after  much  of  this  secondary  bone  had  been  deposited. 
This  figure  is  taken  from  the  margin  of  a  considerable 
absorption  which  was  taking  place  on  the  inner  (lingual) 
surface  of  the  lower  jaw,  about  the  position  of  the  cuspid 
tooth  and  near  the  attachment  of  the  mylo-hyoid  muscle, 
and  was  probably  affecting  some  change  in  the  form  of  the 
bone.  It  shows  the  nature  of  the  absorptive  process. 
Formerly  it  was  supposed  that  the  bone  corpuscles  took 
part  in  the  process,  enlarging  the  capsule  in  which  they 
are  lodged,  but  my  own  observation  shows  quite  con- 
clusively that  they  take  no  part  whatever.  It  is  the  work 
of  the  osteoclasts  entirely,  at  least  in  physiological  absorp- 
tions. 

Intra-membranous  formation  of  bone  occurs  only  in  the 
tabular  bones  of  the  cranium  and  face,  and  possibly  a 
portion  of  the  clavicle.  Its  only  difference  from  the  sub- 
periosteal  formation  is  that  the  bone  arises  de  novo  in 
membrane.  In  all  other  respects  it  is  subperiosteal.  The 
description  of  it  may  therefore  be  limited  to  the  begin- 
nings of  the  formation.  The  form  is  first  laid  down  in 
what  appears  to  be  ordinary  fibrous  membrane,  in  which 


FORMATION   OF  BONE.  53 

there  is  seen  a  tendency  of  the  fibers  to  aggregate  into 
bundles,  which  are  often  condensed  into  fibers  so  large  as 
to  almost  merit  the  name  coarse  fibers.  The  bulk  of  the 
membrane  is,  however,  composed  of  fine  white  connective 
tissue  fibers.  These  decussate  with  considerable  free- 
dom, seemingly  with  a  tendency  to  form  an  irregular 
meshwork.  The  fibroblasts  are  abundant  and  of  the  usual 
form,  and  there  is  seen  quite  a  large  number  of  undevel- 
oped connective  tissue  cells.  At  the  point  where  bone  is 
about  to  be  laid  down,  these  latter  may  be  noticed  to 
aggregate  themselves  together  and  grow  larger,  elongat- 
ing in  a  direction  parallel  to  the  fibers  with  which  they  are 
associated,  but  not  becoming  distinctly  fusiform.  These 
come  to  be  closely  packed  together  at  a  single  point,  and 
they  may  form  a  row  of  some  length,  or  elongated  islands, 
which  take  staining  agents  more  strongly  than  other  tis- 
sues. Passing  these  in  a  direction  toward  the  more 
central  parts  where  bone  formation  has  begun,  it  will  be 
found  that  this  is  laid  down  in  the  center  of  an  exactly 
similar  cluster  of  cells.  As  the  deposit  of  matrix  and 
lime  salts  is  laid  down,  the  cells  seem  to  spread  asunder 
as  if  to  make  room,  while  one,  two  or  more  remain  in  the 
calcified  mass  as  bone  corpuscles.  These  islands  may  be 
found  of  any  dimensions,  from  that  of  the  smallest  island 
in  which  a  single  cell  may  be  distinctly  recognized  as  a 
bone  corpuscle,  to  considerable  areas  of  bone,  all  present- 
ing the  same  characters.  The  usual  forms  of  the  osteo- 
blasts  are  seen  on  the  margins  of  the  formed  bone.  I 
have  represented  one  of  these  islands  in  fig.  28,  from  the 
parietal  bone  of  the  human  fetus  in  which  5,  6,  point  out 
individual  osteoblasts  and  a,  a,  bone  corpuscles.  The  lat- 
ter appear  unusually  large  in  all  of  the  very  young  intra- 
membranous  bone  that  I  have  examined.  The  osteoblasts 
cluster  very  thickly  around  the  margins.  The  fibers  of 
the  membrane  do  not  at  first  give  place  to  the  bone  for- 
mation, but  are  included  within  it,  as  shown  in  the  figure, 


54  FORMATION  OF  BONE. 

and  those  osteoblasts  that  lie  at  the  ends  of  the  formation 
are  apt  to  present  their  ends  to  it,  seemingly  constrained 
to  this  position  by  the  presence  of  the  fibers,  as  in  the 
attached  periosteum.  Different  islands  present  much  dif- 
ference as  to  the  included  fibers,  some  having  very  few, 
while  others,  as  the  one  chosen  for  illustration,  have 
many  and  the  effect  of  these  on  the  disposition  of  the 
cells  around  the  margins  is  plainly  apparent.  For  a  little 
way  outside  the  layer  of  osteoblasts  that  are  in  contact 
with  the  formed  bone,  the  developing  cells  are  thickly 
placed,  and  are  evidently  destined  to  become  osteoblasts. 
The  islands  of  bone  thus  formed  grow  into  spiculse  and  in 
time  unite  with  others  in  the  neighborhood,  and  at  first 
form  a  kind  of  bony  latticework,  the  openings  in  which 
are  finally  filled  to  form  the  complete  bone.  This  is  then 
extended  until  joined  to  its  neighbors  by  suture. 


CHAPTER  VII. 

GBOWTH   OF    BONE    UNDER    TENDINOUS    ATTACHMENTS — 
INTRA-CARTILAGINOUS  FORMATION   OF   BONE. 

As  we  have  seen,  in  the  more  rigidly  attached  forms 
of  the  periosteum,  where  the  fibers  are  very  thickly  set, 
the  growth  of  bone  is  so  modified  that  there  is  no  forma- 
tion of  Haversian  canals  by  the  growth  of  spiculse  and 
arching  over,  but  the  bone  is  deposited  in  a  solid  surface 
and  afterwards  burrowed  out  for  the  formation  of  these 
canals.  This  kind  of  fibrous  investment  of  the  surface  of 
the  bone  is  the  limit  at  which  osteoblasts  appear  on  the 
growing  surface.  At  the  points  of  attachment  of  tendons 
the  strong  fibrous  bursse,  no  osteoblasts  appear  on  the 
surface  of  the  bone,  and  its  extension  by  growth  under 
these  conditions  is  effected  upon  a  different  plan.  This 
is  accomplished  by  the  projection  of  Haversian  canals, 
from  the  bone  beneath  into  the  tendon,  dissolving  a  por- 
tion of  the  substance  of  this,  and  depositing  Haversian 
bone  on  the  walls  of  these  canals. 

I  present  in  fig.  29  an  illustration  of  this  process  as 
seen  at  the  attachment  of  Tendo  Achillis.  The  section 
is  cut  from  a  young  lamb  lengthwise  of  the  tendon  fibers. 
The  large  fibers  of  the  tendon  are  represented  at  A.  For 
a  little  space  in  advance  of  the  bony  formation  these  are 
partially  converted  into  fibre-cartilage,  and  the  cartilage 
cells  are  shown  mostly  between  them.  The  fibers  of  the 
tendon  are,  however,  easily  separated  with  needles  down 
very  close  to  the  new  bone.  Indeed,  although  the  cells 
appear  as  shown  in  the  illustration,  the  tendon  does  not 
otherwise  appear  to  be  cartilaginous. 

At  5,  Haversian  canals,  or  at  least  capillary  loops, 
grow  out  from  the  bone  beneath  and  penetrate  the  fibers, 

55 


56         1NTRA-CARTILAGINOTTS   FORMATION    OF   BONE. 

removing  their  substance.  A  number  of  these  are  seen  in 
the  figure.  This  growth  presents  absorption-cells  similar 
to  those  met  with  in  the  absorption  of  bone,  but  they  do 
not  seem  to  attain  so  large  a  size,  and  react  differently  to 
staining  agents,  which  seems  to  indicate  that  there  is 
some  chemical  difference  between  them.  Indeed,  I  have 
found  some  difficulty  in  so  staining  these  cells  as  to  differ- 
entiate them  clearly.  They  may  be  made  out,  however, 
by  high  powers,  if  the  sections  are  sufficiently  thin,  with- 
out staining.  With  these  absorption-cells  many  embryonal 
elements  are  associated,  in  such'  a  manner  as  to  very 
effectually  obscure  them  if  there  is  much  thickness.  After 
this  process  of  absorption  has  proceeded  for  a  certain 
space,  in  advance  of  the  surface  of  the  bone,  the  pro- 
cesses going  on  within  the  new  canals  are  changed. 
Osteoblasts  take  the  place  of  the  absorption-cells,  and 
bone  is  laid  down  upon  the  walls  of  the  excavation.  This 
is  shown  at  D,  D,  while  e?,  c?,  c,  show  the  Haversian  canals. 
These  are  older  portions  of  the  Haversian  canals,  and  it 
will  be  noted  that  the  bone  is  formed  upon  or  laid  against 
the  tendon  fibers,  which  here  are  more  or  less  calcified,  or 
infiltrated  with  lime  salts.  Everywhere  along  the  sides 
of  these  formations  of  bone  will  be  seen  the  bay-like 
forms  due  to  the  absorbent-cells.  The  growth  is  com- 
posed entirely  of  Haversian  bone.  The  penetration  of 
the  tendon  by  the  individual  canals  is  not  always  in  the 
line  of  its  fibers.  Though  in  a  general  sense  it  is  so,  indi- 
vidual canals  are  often  seen  to  diverge  very  considerably 
from  this  line.  In  the  examination  of  sections  in  extenso, 
it  is  found  that  these  canals  branch  in  various  directions 
into  the  tendon,  and  that  new  canals  are  formed  very  fre- 
quently by  the  absorbents  piercing  the  sides  of  the 
Haversian  systems  formed,  and  starting  out  in  new  direc- 
tions. 

It  will  be  noticed  that  there  is  always  a  very  large 
portion  of  the  fibers  of  the  tendon  left  attached  to  the 


INTBA-CARTILAGINOUS   FORMATION  OF  BONE.  57 

formed  bone.  Were  it  otherwise,  the  strength  of  the 
attachment  of  the  tendon  might  be  seriously  impaired. 
Really  many  of  the  fibers  continue  to  penetrate  deeply 
among  the  Haversian  systems,  as  seen  at  E.  These  are 
finally  removed  by  the  formation  of  new  Haversian  canals, 
by  which  the  new  bone  soon  becomes  very  much  cancel- 
lated, though  we  may  find  occasional  isolated  patches 
deep  in  the  formed  bone. 

The  conversion  of  the  articular  cartilages  into  bone, 
during  the  lengthening  of  the  shaft,  is  a  process  almost 
precisely  similar  to  that  just  described,  so  far  as  the 
absorption  and  removal  of  the  cartilage,  and  the  deposit 
of  the  new  bone  is  concerned.  There  is,  however,  a 
marked  change  in  the  cartilage,  which  appears  to  be  a 
preparation  of  it  for  removal  and  the  formation  of  bone. 
I  should  state  here,  however,  that  there  are  two  quite 
distinct  modes  in  the  replacement  of  cartilage  by  bone, 
the  one  taking  place  in  the  articular  cartilages  of  the 
long  bones,  and  probably  in  the  whole  of  the  short  bones, 
while  the  other  is  confined  to  the  shafts  of  the  tubular 
bones.  I  do  not  wish  to  confound  these  two  forms  of 
the  process,  as  has  so  frequently  been  done  in  our  past 
literature. 

I  present  an  illustration  from  the  tibia  of  a  kitten, 
representing  the  position  of  these  two  forms  soon  after 
the  process  in  the  epiphysis,  fig.  32.  The  process  of  ossi- 
fication has  begun  in  the  diaphysis  early  in  fetal  life,  and 
is  far  advanced  before  the  beginning  is  made  in  the 
epiphysis.  The  subperiosteal  growth  of  bone  is  begun 
before  the  beginning  of  the  intra-cartilaginous,  and  con- 
tinually precedes  it.  e,  c,  Represent  the  subperiosteal 
deposit,  the  advance  of  which  terminates  in  the  periosteal 
notch  e,  e.  It  will  be  noted  that  a  thin  layer  of  subperi- 
osteal bone  passes  up  to  this  notch.  /,  Marks  the  begin- 
ning of  change  in  the  cartilage  cells  represented  in  fig. 
33,  and  <7,  the  line  of  the  absorption  of  the  cartilage  and 
8 


58        INTRA-CARTILAGINOUS   FORMATION   OF   BONE. 

the  point  of  the  diaphysal  intra-cartilaginous  formation  of 
bone.  The  darkened  portions  c?,  represent  the  bone  mar- 
row, and  the  light  portions  the  bone  formed,  which  latter 
occupies  but  a  small  part  of  the  area.  At  a,  the  cartilagi- 
nous head  of  the  bone  is  seen,  with  the  beginning  of  the 
process  of  epiphysal  ossification  at  A. 

The  changes  in  the  epiphysal  cartilages  will  appear 
somewhat  differently  in  the  same  animal  at  different  ages. 
In  following  up  the  examination  of  sections,  cut  through 
the  center  of  the  head  of  the  tibia,  for  instance,  beginning 
with  the  surface  of  the  articular  cartilage,  this  will  be 
found  to  consist  almost  entirely  of  fine  white  fibers 
(fibrous  tissue),  arranged  perpendicular  to  the  surface, 
and  lying  very  compactly  together.  A  little  inward  from 
the  surface  very  small  cells  come  into  view,  and  if  the  sec- 
tion be  sufficiently  thin  it  will  be  noted  that  these  lie 
between  the  fibers.  Still  proceeding  inward,  the  cells 
become  larger,  and  the  fibers  more  indistinct.  In  many 
instances  the  fibers  seem  to  gather  into  groups  or  bun- 
dles, and  terminate ;  in  others,  they  simply  fade  away 
into  the  cartilage.  Farther  inward,  nothing  but  the 
clear  ground  substance  of  the  cartilage  studded  with  its 
cells,  is  seen.  These  cells  are  small  at  first  and  single, 
but  they  grow  larger,  and  soon  we  find  two  together,  and 
finally  three  or  four,  and  perhaps  more,  which  seem  to 
occupy  a  single  capsule. 

At  this  point  a  great  variety  of  appearances  may  be 
found  in  the  examination  of  the  changes  as  they  occur  in 
animals  at  different  ages.  In  fig.  31,  I  present  an  illus- 
tration from  the  head  of  the  tibia  of  a  lamb  about  two 
months  old,  which  shows  these  cells  as  flattened  and  in 
distinct  rows.  In  this  case  the  change  of  the  cartilage  to 
bone  is  well  advanced.  If  it  had  been  examined  at  an 
earlier  age,  especially  before  the  junction  of  the  diaphysal 
with  the  epiphysai  bone  formation,  these  rows  of  cells 
would  not  have  been  found,  but  instead  the  enlargement 


INTRA-CARTILAGINOUS  FORMATION   OF  BONE.         69 

of  the  cells  would  have  been  found  proceeding  regularly, 
while  they  remain  scattered  without  order,  i.  e.,  without 
falling  into  rows.  Although  I  have  not  seen  the  actual 
.division  of  cells,  and  know  of  no  one  who  claims  to  have 
done  so,  there  can  be  no  reasonable  doubt  that  we  have 
been  following  the  active  results  of  growth,  not  only  of 
the  individual  cells,  but  of  the  multiplication  of  the  cel- 
lular elements  by  division.  After  passing  inward  from 
this  formation  of  rows,  it  is  found  that  this  arrangement 
is  lost,  and  the  cells  are  again  scattered  over  the  field 
without  order  of  arrangement,  as  shown  in  the  figure,  and 
that  the  space  between  them  has  become  much  greater. 
At  this  point  the  cartilage  becomes  infiltrated  with  lime 
salts,  and  all  activity  within  it  ceases.  This  statement 
should,  however,  be  qualified,  in  so  far  as  to  say  that  in 
the  younger  articular  cartilages,  when  the  process  of 
change  is  just  beginning,  only  the  matrix  becomes  calci- 
fied, the  cells  remaining  soft ;  but  in  such  as  that  from 
which  our  illustration  was  taken,  the  cell  bodies  are  also 
calcified. 

The  process  of  absorption  of  the  cartilage  is  begun  by 
the  perforation  to  its  center  of  one  or  more  canals.  These 
then  spread  out  for  a  considerable  space,  showing  at  first 
no  disposition  to  the  formation  of  bone.  The  cartilage  is 
absorbed,  and  replaced  by  tissue  of  a  primitive  fetal  type. 
Soon,  however,  short  canals  begin  to  radiate  from  this 
central  cavity,  and  after  proceeding  for  a  space,  the  pro- 
cess of  absorption  ceases.  Osteoblasts  then  develop  along 
the  walls  of  the  space  opened,  and  begin  to  lay  down  bone 
upon  the  cartilage.  While  this  is  in  progress,  new  canals 
are  being  opened  at  other  points,  which  in  succession 
receive  deposits  of  bone  upon  their  walls.  In  this  pro- 
cess the  new  bone  is  laid  directly  upon  the  cartilage,  and 
in  the  successive  burrowings,  very  nearly  all  of  the  cartil- 
age is  removed,  but  often  a  small  remainder  will  be  found 
at  some  distance  from  the  margin  where  the  absorption  is 


60        INTRA-CARTILAGINOUS   FORMATION   OF  BONE. 

in  progress,  in  the  central  part,  perhaps,  of  some  portion 
of  the  newly  formed  bone.  However,  the  first  bone  laid 
down  is  usually  removed  by  absorption  after  a  time,  so 
that,  in  the  end,  all  of  the  cartilage  is  absorbed.  Indeed, 
at  first — that  is,  in  very  young  animals — when  the  absorp- 
tion of  the  cartilage  is  still  confined  to  its  central  parts, 
the  Haversian  canals  formed  remain  very  large,  only  a 
thin  stratum  of  bone  being  deposited  upon  their  walls. 
At  a  more  advanced  age,  the  deposit  of  bone  is  greater, 
though  at  all  times  it  remains  quite  cancellous. 

During  the  earlier  period  of  absorption  the  cells  of  the 
cartilage  remain  soft,  and  the  effect  of  this  condition 
influences  the  absorptive  process,  for  as  soon  as  the  wall 
of  one  of  these  is  opened  the  cell  body  seems  to  escape,  at 
least  it  disappears,  and  the  place  is  occupied  by  fetal  tissue 
of  the  same  type  as  that  which  fills  the  Haversian  canals 
in  the  immediate  neighborhood.  There  has  been  much 
speculation  as  to  the  destiny  of  the  cartilage  cells,  some 
supposing  that  they  form  osteoblasts  by  a  process  of 
division,  but  it  seems  now  so  well  settled  that  they  simply 
disintegrate  before  the  absorbents  that  it  is  hardly  neces- 
sary to  discuss  the  point.  I  may  say  that  I,  like  many 
others  who  have  essayed  to  examine  this  point,  have  been 
unable  to  see  just  what  does  become  of  them.  They 
seem  simply  to  disappear. 

In  older  animals,  when  this  portion  of  the  cartilage  in 
its  entirety,  including  the  cells,  becomes  calcified  the  pro- 
cess of  absorption  is  studied  to  much  better  advantage ; 
for  before  this  time,  the  walls  upon  which  the  absorbents 
act  are  continually  being  broken  by  the  opening  of  the 
capsules,  with  the  protrusion  of  the  fetal  cells  of  the 
Haversian  canals  into  them,  and  these  are  so  numerous 
as  to  obscure  other  phenomena.  But  now  the  absorption 
of  the  calcified  cells  proceeds  in  the  same  orderly  way  as 
in  the  matrix  itself,  and  the  wall  acted  upon  by  the  absor- 
bent cells  is  continuous  around  the  new  Haversian  canal, 


INTRA-CARTILAGINOUS   FORMATION   OF   BONE.         61 

as  shown  in  the  illustration.  Here  we  may  trace  the 
work  of  the  chondroclasts,  both  bv  the  presence  of  these 
cells,  and  the  indentations,  or  bay-like  cavities  left  in  the 
walls  of  the  cartilage,  both  in  the  new  Haversian  canals, 
in  which  bone  is  not  yet  deposited,  and  in  those  in  which 
it  is,  as  is  shown  in  the  figure.  In  order  to  illustrate  this 
to  better  advantage,  I  have  prepared  a  representation  of 
a  single  one  of  these  absorbed  spaces,  or  new  Haversian 
canals  in  fig  30,  using  for  the  purpose  a  high  power,  in 
which  the  chondroclasts,  and  their  relation  to  the  liquefy- 
ing cartilage  can  be  studied  to  better  advantage.  These 
are  identical  in  form  and  function  with  the  osteoclasts, 
and  here  should  be  termed  chondroclasts,  to  indicate  their 
position,  as  on  the  same  principle  we  call  them  osteoclasts 
when  found  applied  to  the  solution  of  bone.  Here  we 
find  them  applied  in  precisely  the  same  way,  and  produc- 
ing similar  results.  Touching  the  question  of  the  destiny 
of  the  cartilage-cells,  I  may  say  that  under  the  conditions 
last  described,  I  have  often  found  one-half  of  one  of  these 
cut  away  by  the  absorbents,  while  the  other  remained 
in  its  matrix,  which,  it  seems  to  me,  definitely  settles  the 
question  of  the  destiny  of  these  cells,  when  in  this  condi- 
tion at  least.  They  are  simply  absorbed  in  the  same  way 
as  the  cartilage  matrix. 

The  regular  placement  of  the  chondroclasts,  in  the 
absorption  of  the  articular  cartilage,  can  not  well  be  made 
out  before  the  calcification  of  the  cartilage-cells.  Their 
presence,  however,  is  sufficiently  manifest.  They  may  be 
found  about  the  walls  of  the  liquefying  cartilage,  at  many 
points,  soon  after  the  beginning  of  the  process,  but  there 
seems  to  be  no  regularity  whatever  in  their  distribution, 
so  that  in  studying  the  process  in  this  stage  alone,  one 
could  not  easily  make  out  that  these  were  the  principal 
agents  of  solution.  Indeed,  it  is  extremely  doubtful 
whether  they  are  the  only  agents  of  this  process,  as  we 


62         INTRA-CARTILAGINOTJS   FORMATION   OF    BONE. 

shall  see  in  the  study  of  that  form  which  takes  place  in 
the  shafts  of  tubular  bones. 

The  articular  cartilages  are  continuously  increased  by 
growth  and  division  or  multiplication  of  their  cells,  and 
a.s  continuously  absorbed  and  replaced  by  bone  until  the 
process  ceases  with  the  cessation  of  growth  .at  maturity. 
This  growth  of  the  cartilage  represents  the  lengthening  of 
the  shafts  of  the  bones.  This  lengthening  takes  place 
mostly  in  the  diaphysal  form  of  the  process,  until  that 
ceases  by  junction  with  the  epiphysal,  and  it  is  at  this 
time  that  we  find  the  cartilage-cells  of  the  epiphysis  fall- 
ing into  rows  before  the  advance  of  the  absorbents.  It 
seems  therefore  that  the  lengthening  of  the  bones  takes 
place  mostly  by  the  growth  of  the  cartilage  in  this  partic- 
ular form,  which  will  be  described  more  particularly 
later. 

As  has  been  said,  the  greater  part  of  the  skeleton  is- 
first  laid  down  in  cartilage.  This  is  true  of  all  the  long 
bones,  and  at  a  later  period  this  provisional  cartilage  i& 
replaced  by  bone.  The  mode  by  which  this  change  is 
made  in  the  diaphysis  of  the  tubular  bones,  is  distinctly 
different  from  that  in  the  epiphysis.  This  relates  espe- 
cially to  that  portion,  which  is  at  a  later  period  converted 
into  the  bone  marrow,  which  really,  at  this  time,  includes 
the  whole  of  the  shaft  of  the  bone.  The  beginning  of  this 
process  is  seen  first,  near  the  middle  of  the  length,  and  in 
the  central  part  of  the  cartilage  representing  the  bone. 
Here  the  cartilage  cells  are  seen  to  enlarge,  and  appar- 
ently move  apart,  so  that  in  addition  to  the  enlargement 
of  the  cells,  there  is  also  an  augmentation  of  the  matrix 
as  well.  Just  how  the  increase  of  this  matrix  occurs  is 
not  well  understood.  Indeed,  I  may  say  that  although 
the  processes  taking  place  in  the  growth  of  the  cartilage 
have  long  since  strongly  attracted  the  attention  of  histol- 
ogists,  they  have  not  yet  been  made  out  satisfactorily. 
The  fact  of  growth  in  this  portion,  and  decided  increased 


INTRA-CARTILAQINOUS   FORMATION   OF   BONE.         63 

activity  over  that  of  the  other  parts  of  the  cartilage  is 
stfficiently  apparent  in  the  facts  just  stated,  and,  at  the 
same  time,  there  is  a  slight  but  decided  enlargement  of 
the  diameter  at  this  point,  though  the  principal  growth  is 
in  the  direction  of  the  length  of  the  shaft.  At  this  time 
a  change  becomes  manifest  upon  the  surface  of  the  en- 
larged portion.  The  internal  portion  of  the  perichondri- 
um  is  composed  of  moderately  fine  white  fibers  running 
for  the  most  part  lengthwise  of  the  cartilage,  and  lying 
quite  compactly  together.  Between  these  the  cartilage 
cells  arise ;  first  as  very  fine  white  granular  elongated 
points  not  unlike  the  fusiform  cells  of  white  fibrous 
tissue.  Successively  they  grow  larger,  as  we  proceed  in- 
ward from  the  surface,  and  finally  the  fibers  fade  away 
into  the  fully  formed  cartilage,  without  any  very  strict 
limiting  line.  Occasionally  however,  the  change  to  car- 
tilage is  more  abrupt,  and  there  seems  to  be  a  more  or  less 
distinct  limiting  line  between  the  perichondrium  and  the 
cartilage.  Especially  will  this  be  the  case  in  a  cross  sec- 
tion, or  if  the  section  is  somewhat  diagonal.  Within  the 
borders  of  the  growing  cartilage,  the  cells  are  still  very 
nearly  of  the  same  form,  but  larger,  and  as  we  proceed 
inward,  they  gradually  assume  the  usual  form  of  the  car- 
tilage cells.  Now  at  the  point,  where  the  cartilage  cells 
have  enlarged  in  the  central  part,  and  the  enlargement  of 
the  diameter  of  the  cartilage  is  seen,  a  change  takes  place 
in  the  inner  layers  of  the  perichondrium.  Fetal  cells, 
small  round  or  oval  cells,  are  deposited  here  and  gradu- 
ally separate  the  cartilage  and  perichondrium.  This  por- 
tion assumes  a  distinctly  cellular  type,  and  if  the  pro- 
cesses are  carefully  followed,  with  high  powers,  in  suffi- 
ciently thin  sections,  it  will  become  evident  that  some  of 
these  cells  become  fusiform  (fibroblasts)  and  are  proceed- 
ing to  the  development  of  white  fibrous  tissue,  while 
others  grow  larger,  and  become  arranged  along  the  mar- 
gin of  the  cartilage.  The  appearance  of  a  layer  of  bone 


64  INTRA-CARTILAGINOUS  FORMATION   OF  BONE. 

deposited  on  the  surface  of  the  cartilage  soon  disting- 
uishes these  as  osteoblasts.  Here  it  is  perfectly  evident 
that  an  inner  layer  of  periosteum  has  had  a  de  novo  de- 
velopment. This  portion  is  evidently  not  a  change  of 
the  perichondrium  into  periosteum.  The  change  in  the 
outer  layer  of  coarse  fibers  is  not  so  clear,  for  though 
some  change  is  gradually  taking  place  in  the  form  and 
disposition  of  the  fibers,  it  does  not  appear  to  be  the  sub- 
stitution of  a  newly  developed  tissue,  as  is  the  case  in  the 
inner  layer.  Such  is  the  beginning  of  the  deposit  of  sub- 
periosteal  bone  upon  the  cartilaginous  matrix,  and  this 
goes  on  coincidentally  with  the  changes  occurring  within 
the  central  portions;  for  while  the  changes  just  described 
are  in  progress  several  capillaries  have  pierced  the  form- 
ing layer  of  bone,  and  found  their  way,  by  a  process  of 
absorption,  to  the  very  center  of  the  cartilage,  where  the 
cells  are  most  enlarged.  Here  the  capillary  loops  en- 
large, melting  down  the  cartilage  about  them  and  forming 
a  central  cavity.  This  is  filled  with  tissue  of  the  fetal 
type,  in  which  very  small  round  cells  (marrow  cells)  are 
especially  abundant.  These  are  evidently  leucocytes  de- 
posited here  from  the  capillary  vessels.  While  these  pro- 
cesses are  in  progress,  further  changes  have  occurred  in 
the  cartilage  itself.  The  cartilage  cells  throughout  its 
thickness  become  enlarged.  This  change  spreads  either 
way  toward  the  extremities  for  space,  and  these  enlarged 
cells  are  seen  to  have  fallen  somewhat  irregularly  into 
rows,  which  coincide  with  the  long  axis  of  the  cartilage. 
Very  soon,  or,  we  may  say,  coincidentally  with  these 
changes,  areas  of  proliferation  of  cartilage  cells  are  estab- 
lished on  either  side  (toward  either  end  of  the  future 
bone)  of  these  enlarged  cells,  which  are  maintained 
throughout  the  period  of  the  removal  of  the  cartilage,  and 
its  replacement  by  bone.  In  fig.  33  I  present  an  illustra- 
tion from  a  pigmented  section  cut  from  the  femur  of  a 
kitten,  of  the  changes  taking  place  toward  one  end  of  the 


INTRA-CARTILAGINOUS   FORMATION   OF    BONE.         65 

future  bone,  after  considerable  progress  lias  been  made  in 
the  process.     At  A,  the  unchanged  cartilage  is  seen,  and 
the  progressive  changes  are  represented  between  that  and 
the  letter  jF,  which  latter  shows  a  portion  of  the  bone- 
forming  area.     Between  A  and  B  the  cartilage  cells  sud- 
denly become  smaller,  and  the  supposition  is  that  this  is 
by   subdivision.     In   this   process   they   fall    into   rows, 
which  is  continued  to  E.     It  will  be  noted  that  very  soon 
the  cells  grow  larger,  and  continue  to  do  so,  down  as  far 
as  the  letter  Z>.     In  the  study  of  complete  sections,  it  is 
found  that   this   growth  is  mostly  in  the  direction  of  the 
length  of  the  bone.     Indeed,  this  is  very  apparent  in  the 
illustration,  for,  it  will  be  noted,  that  at  .5,  the   cells  are 
very   much   flattened,  so  that  in  the  lengthwise  section 
they  appear  banana-shaped  with  rather  a  disposition  to 
enlarge  at  one  end  ;  and,  in  the   enlargement  from  B  to 
(7,  they  become  somewhat  rounded,  mostly  by  gaining  in 
breadth.     At  0  also  the  capsules  that  enclose   the  indi- 
vidual cells  are  more  and  more  separated  in  the  direction 
of  the  forming  bone.     This  represents  the  growth  of  the 
shaft  of  the  bone  in  length,  for  after  the  osseous  sub- 
stance is  once  formed,  it  does  not  increase  in  dimensions 
by  interstitial  growth.     The    increment   is  always  to  the 
ends,  first  in  cartilage,  then  by  the  process  of  growth  rep- 
resented in  the  illustration.     In  the   region  of   D,  it  will 
be  seen  that  the  nuclei  (the  transparent  portion   of  the 
cell  fills  the  capsule)  are  diminishing  in  size  and  becom- 
ing rather   ragged  in    outline.     This    is  undoubtedly   a 
mark  of  degeneration  in  the  cell,  and  it  will  be  noted  that 
the  growth  of  the  cells  ceases  from  about  this  point.  They 
become  passive,  and  take   no  further  active   part  in  the 
processes  that  are  going  on  ;  unless  it  be  a  slight  advance 
toward   disintegration,   as  indicated   by  the   progressive 
diminution  of  the  nuclei.     Occasionally  a  globular  form 
will  be  seen  occurring  in  the    central  part  of  the  nucleus 
at   this   time,  that   closely   resembles   the   marrow   cells 
9 


66        INTRA-CARTILAGINOTJS   FORMATION   OF   BONE. 

which  appear  so  abundantly  after  the  capsules  of  the  car- 
tilage cells  are  broken  into  by  the  absorptive  process  ;  but 
I  have  never  seen  more  than  a  single  one  of  these  in  a 
cell,  and  must  suppose  that  this  is  either  a  nucleolus,  or, 
that  it  is  an  accidental  dropping  together  of  material  of 
the  disintegrating  nucleus.  In  the  region  between  D, 
and  E,  that  portion  of  the  mass  that  forms  the  walls  of 
the  capsules,  in  which  the  cells  are  imbedded,  is  under- 
going the  process  of  calcification,  or  infiltration  with  lime 
salts.  At  least,  this  is  the  general  opinion  of  those  who 
have  examined  the  subject  with  reference  to  this  point. 
My  own  examinations  do  not  enable  me  to  determine  it. 
The  whole  of  the  cartilage,  from  the  region  B  down,  is 
much  more  transparent  than  the  cartilage  in  which  the 
changes  have  not  yet  begun,  and  this  difference  is  ren- 
dered much  more  prominent  by  pigmenting.  In  this  pro- 
cess the  cell  bodies  remain  absolutely  transparent  as 
represented  in  the  illustration.  This  is  entiiely  different 
from  the  epiphysal  cartilage  while  undergoing  this 
change.  In  these  the  whole  of  the  cartilate  takes  the 
pigment  in  a  marked  degree,  and  this  is  true  when  the 
two  forms  are  included  in  the  same  section,  as  I  have 
often  had  them  toward  the  end  of  the  process  of  ossifica- 
tion. They  also  react  differently  to  other  stains.  This 
fact  seems  to  show  plainly  that  there  is  some  chemical 
difference  in  the  structure,  to  which  this  difference  of 
reaction  is  due,  but  as  yet  I  am  ignorant  as  to  what  this 
difference  may  be. 

The  most  interesting  part  of  the  process  is  that  taking 
place  at  E.  Here  we  find  that  the  walls  of  the  capsules, 
facing  toward  the  central  part  of  the  length  of  the  shaft, 
are  successively  disappearing  before  the  advance  of  a 
growth  of  fetal  tissue,  and  that  the  remaining  or  lateral 
walls  of  these  same  capsules  become  so  many  tubes  in 
which  this  growth  advances.  Some  of  these,  indeed,  are 
also  broken  down,  merging  two  into  one,  frequently 


INTRA-CARTILAGINOUS   FORMATION   OF   BONE.         67 

making  larger  tubes.  But  for  a  space  the  greater  num- 
ber of  them  remain.  This  occurs,  not  in  a  few  of  the 
rows  of  cells  that  form  the  shaft  of  the  cartilage,  but  in  all 
of  them  together,  generally  forming  very  nearly  a  straight 
line  through,  or  as  seen  in  sections,  across  the  shaft  of 
the  cartilage.  That  is  to  say,  presenting  a  solid  advance 
which  includes  the  whole  thickness  as  represented  in  Fig. 
33.  There  are  no  radiating  canals,  as  seen  in  the 
absorption  of  the  epiphysal  cartilages,  or  in  the  absorp- 
tion of  tendons,  ligaments  and  bursse.  (Compare  with 
Figs.  29  and  31.) 

But  before  speaking  further  of  the  process  of  absorp- 
tion, let  us  examine  the  tissue  that  is  taking  the  place  of 
the  cartilage.  At  h,  are  seen  the  round  cells  (marrow 
cells)  that  are  very  generally  advanced  to  fill  the  capsules 
from  which  the  cells  seem  to  escape,  as  soon  as  the  cap- 
sules are  opened.  These  are  seen  everywhere  in  the  mass 
of  fetal  tissue,  and  they  are  often  so  abundant  as  to  ren- 
der the  observation  of  the  other  cellular  elements  diffi- 
cult. Furthermore,  they  are  liable  to  be  scattered  over 
the  other  parts  of  the  section,  in  the  course  of  the  prepa- 
ration, and  lead  to  confusion,  unless  special  care  is  taken. 
On  the  right  hand  of  the  figure  some  of  the  tissue  has 
been  lost,  but,  in  the  other  portions,  it  will  be  seen  that 
these  round  cells  are  filling  the  capsules  opened.  At  JV, 
one  seems  to  have  been  just  opened,  and  these  cells  seem 
in  the  act  of  crowding  into  the  aperture.  At  0,  are 
pointed  out  fusiform  or  oval  cells,  applied  closely  to  the 
remaining  walls  of  the  capsules  which,  it  will  be  observed, 
extend  to  the  lower  end  of  the  figure,  and  are  marked 
with  the  letter  p  at  various  points.  At  m,  w,  m,  TW,  are 
seen  the  cellular  elements  and  fibers  of  the  blood  vessels, 
which  are  extended  into  each  one  of  the  opened  tubes. 
/,  Points  out  osteoblasts  applied  to  the  remaining  walls  of 
cartilaginous  matrix,  upon  which  no  bone  has  yet  been 
deposited.  These  are  seen  also  in  other  parts  of  the 


68        INTRA-CARTILAGINOUS  FORMATION   OF  BONE. 

figure.  No  deposit  of  bone  is  seen  usually,  until  the 
space  of  several  cartilage  cells  beyond  the  point  of 
absorption  has  been  reached,  but  at  K,  K,  JT,  K,  is  seen 
deposited  on  the  walls  of  the  tubes  a  layer  of  bone  which 
is  in  turn  covered  with  osteoblasts.  The  new  bone  is 
deposited  upon  the  remains  of  the  cartilage,  partially  fill- 
ing up  the  tubes  formed  by  the  opening  of  the  capsules 
of  the  cartilage  cells. 

We  may  now  return  to  the  absorption  area,  repre- 
sented at  E.  In  this  absorption  I  have  been  unable  to 
identify  a  single  well  marked  choiidroclast,  applied  to  the 
opening  of  the  capsules  of  the  cartilage  cells.  In  Fig.  33 
all  of  the  capsules  opened  are  partly  destitute  of  cells, 
i.e.,  have  not  yet  filled  up  with  the  advancing  cells,  but  in 
Fig.  34  I  supplement  this  defect,  by  choosing  for  illustra- 
tion a  few  capsules  which  the  fetal  tissue  fills  compactly. 
Here  we  find  both  fusiform  and  marrow  cells  applied  to 
the  boneward  face  of  the  capsules,  sometimes  the  one, 
sometimes  the  other,  or  they  may  be  mixed  together. 
These  fusiform,  eel  Is  have  uniformly  a  well  marked  nuc- 
leus of  irregular  outline,  instead  of  the  pale  round  form 
seen  in  the  chondroclasts  and  osteoclasts,  and  we  see 
apparently  the  same  cells  applied  to  the  remaining  walls 
without  witnessing  any  evidence  of  solution.  The  absorp- 
tion cells  appear  in  great  abundance  a  little  further  away, 
removing  portions  of  the  tube  walls  and  enlarging  the 
channels.  (Fig.  35.) 

The  agents  of  solution  in  this  case  are  probably  the 
small  cells.  It  is  well  known  that  the  leucocytes  develop 
this  power  in  a  marked  degree  in  other  localities.  They 
are  the  agents  of  solution  of  sponge,  in  the  sponge-graft, 
of  animal  membrane  sutures,  ligatures,  and  other  foreign 
substances.  They  are  also  the  principal  agents  of  absorp- 
tion, when  this  process  occurs  in  connection  with  inflam- 
mation. Furthermore,  the  absorption  cells  are  undoubt- 
edly developments  from  the  primary  connective  tissue 


INTRA-CARTILAGINOUS   FORMATION   OP  BONE.         69 

cells,  which  these  round  cells  represent.  They  require 
time  to  make  their  growth,  and  during  this  period  of 
growth  are  exercising  their  peculiar  function,  as  has  been 
shown  on  a  former  page.  It  may,  therefore,  be  assumed 
that  in  the  absorption  we  are  now  considering,  the 
amount  of  tissue  removed  at  one  point  being  only  the 
thin  wall  of  these  capsules,  is  too  small  for  the  devel- 
opment of  chondroclasts  that  will  be  capable  of  satis- 
factory differentiation  from  others  by  microscopic  exami- 
nation. 

As  already  indicated,  the  remaining  walls  of  the 
alveoli  of  the  cartilage  cells  become  the  nidus  for  the 
deposit  of  bone,  at  a  point  removed,  by  the  length  of  a 
few  cells,  from  the  point  of  absorption.  It  will  be  noted 
also  that  the  greater  portion  of  the  matrix  of  the  cartilage 
still  remains,  this  having  already  been  reduced  to  a  very 
small  amount,  by  the  progressive  enlargement  of  the 
cartilage  cells,  as  illustrated  in  fig.  33.  At  a  distance  of 
a  few  cell-lengths  further,  the  absorption  of  this  remain- 
der of  the  cartilage  matrix,  together  with  that  of  the 
greater  part  of  the  bone  first  deposited,  is  in  active  pro- 
gress. This  is  best  seen  in  cross  sections,  fig.  35.  If 
these  are  double  stained  with  hematoxyliri  and  carmine, 
the  remains  of  the  cartilage  will  be  purple,  while  the  bone 
deposited  upon  it  will  be  red,  which  distinguishes  them 
sharply  and  quite  beautifully,  and  at  the  same  time  the 
cellular  elements  are  well  shown.  In  following  up 
serially  cross-sections  prepared  in  this  way,  and  receding 
bone-ward  from  the  point  of  the  beginning  of  bone  form- 
ation, it  will  be  found  that  the  Haversian  canals  are 
enlarged  and  decrease  in  number,  and  in  this  process  all 
or  nearly  all  of  the  remains  of  the  cartilage  is  removed. 
Indeed,  in  the  central  part  of  the  shaft  only  a  little  bone 
is  formed,  and  this  is  all  removed  after  a  time,  to  form  the 
cavity.  Along  the  circumference  the  bony  formation  is 
stronger,  and  is  merged  with  the  subperiosteal  bone  ;  but 


70         INTRA-C ART IL AGIN OUS   FORMATION  OF  BONE. 

even  this  is  also  removed  in  time.  In  all  of  the  central 
portion  of  the  length  of  the  shaft  it  is  not  reformed, 
or  if  so,  it  is  only  to  be  removed  again ;  but  toward  the 
ends  of  the  bone  it  is  replaced  with  more  mature  Haver- 
sian  bone. 

The  processes  of  bone  formation  and  of  its  absorption 
are  going  on  simultaneously  in  a  very  close  proximity.  I 
have  illustrated  this  in  fig.  35,  from  a  cross  section  of  the 
rib  of  a  young  kitten,  at  some  little  distance  boneward 
from  the  point  where  ossification  begins,  d,  Represents 
a  few  Haversian  canals  cut  across.  5,  J,  Point  out  the 
bone,  and  a,  the  remains  of  the  cartilage  matrix,  which, 
when  there  has  been  no  absorption  of  the  bone  formed, 
lies  centrally  in  the  irregular  rings  of  bone.  Osteoblasts 
appear  over  a  large  part  of  the  surface,  but  at  some 
points  absorption  is  in  progress;  the  osteoclasts  are 
indicated  by  the  letter  c.  By  the  absorption  overbal- 
ancing the  deposit  of  bone,  the  space  is  gained  for  the 
bone  marrow. 

In  all  of  these  varying  phases  of  bone  formation,  it 
will  be  noted  that  the  active  agents  are  the  osteoblasts. 
These  seem  to  be  developed  in  the  inner  layer  of  the  peri- 
osteum, or  with  equal  facility  in  the  tissue  that  fills  the 
Haversian  canals,  or  the  endosteum.  They  are  therefore 
not  peculiar  to  the  periosteum,  but  belong  rather  to  the 
surface  of  the  bone,  whether  this  surface  be  an  external 
or  an  internal  one. 


CHAPTER  VIII. 

THE  PEEIDENTAL  MEMBRANE. 

The  peridental  membrane  comprises  that  tissue  which 
intervenes  between  the  root  of  the  tooth  and  the  bony 
walls  of  its  alveolus.  It  has  received  various  names  from 
time  to  time,  as  alveolo-dental  membrane,  dental  perios- 
teum, alveolo  -  dental  periosteum,  pericementum,  etc. 
The  office  of  this  membrane  may  be  regarded  as  threefold 
— functional,  physical  and  sensory.  It  is  functional  in  so 
far  as  it  is  the  place  of  the  development  of  the  osteoblasts, 
which  build  portions  of  the  alveolar  walls,  and  the 
cementoblasts,  which  build  the  cementum.  These  cells 
seem  to  be  received  into  the  fibrous  meshes  of  this  mem- 
brane from  the  blood  streams  as  leucocytes  or  amoeboid 
cells  and  here  undergo  their  development,  or  that  differ- 
entiation which  fits  them  for  the  building  of  bone  on  the 
one  side,  and  the  building  of  cementum  on  the  other. 
During  this  development  they  become  allied  to  their 
respective  places,  i.  e.,  the  surface  of  the  bone  and  the 
surface  of  the  cementum. 

The  physical  function  is  the  fixation  of  the  tooth  in  its 
position,  a  passive  function  which  is  performed  by  the 
fibrous  elements.  These  fibers,  which  I  shall  designate 
as  the  principal  fibers,  form  the  bulk  of  the  tissue  of  the 
membrane,  and  their  ends  are  fixed  in  the  cementum  of 
the  tooth's  root  on  the  one  side,  and  in  the  bone  which 
forms  the  walls  of  the  alveolus  on  the  other,  and  are  thus 
stretched  across  the  intervening  space  in  various  direc- 
tions, and  in  such  a  manner  as  to  swing  the  tooth  in  its 
socket. 

The  sensory  function  is  supplied  by  an  abundance  of 
nerves  which  enter  the  membrane  from  every  direction 

71 


72  THE   PERIDENTAL   MEMBRANE. 

through  the  walls  of  the  alveolus,  at  the  apical  space,  and 
by  way  of  the  gingival  border  below*  the  rim  of  the 
alveolus. 

Besides  the  osteoblasts  and  cementoblasts,  the  mem- 
brane presents  various  cellular  elements:  such  as  fibro- 
blasts  for  the  augmentation  or  renewal  of  its  fibrous 
tissues ;  osteoclasts  for  the  removal  of  the  walls,  or  por- 
tions of  the  walls  of  the  alveolus  for  the  accommodation 
of  changes  in  the  position  of  the  tooth,  or  of  the  cementum 
for  the  change  of  the  form  of  the  tooth's  root.  These  lat- 
ter seem  to  be  developed  as  occasion  requires,  but  are 
very  generally  present  somewhere  within  the  alveolus. 
Besides  the  cells  mentioned  there  is  always  a  considerable 
number  of  undeveloped  cells  within  the  meshes  of  the 
fibrous  tissue  in  young  subjects,  but  not  very  many  in  the 
old.  There  is  also  a  set  of  lymphatics  which  are  peculiar 
to  this  membrane.  They  occur  in  great  abundance 
immediately  surrounding  the  cementum  in  young  sub- 
jects, but  are  much  diminished  in  numbers  in  the  old. 

In  many  parts  of  the  membrane  there  is  seen  an  indif- 
ferent inter-fibrous  tissue.  It  is  a  tissue  composed  of 
cells  and  fibers,  not  possessing  very  marked  characters, 
intervening  between  the  principal  fibers  in  many  places, 
especially  where  these  are  large,  and  making  up  the  bulk 
of  the  membrane  in  certain  localities  where  these  are 
absent,  and  accompanying  the  blood-vessels  and  nerves. 

The  form  of  the  membrane  is  such  as  to  closely  invest 
the  root  of  the  tooth  and  fill  its  alveolus,  but  it  does  more 
than  this,  for  it  invests  the  tooth  lower  down  than  the 
lowest  border  of  the  alveolar  wall.  The  membrane  may 
conveniently  be  divided  into  three  divisions:  the  apical, 
that  portion  surrounding  the  immediate  apex  of  the  root, 

*  In  the  descriptions  which  follow,  the  tooth  will  be  regarded  as 
a  cone  of  which  the  end  of  the  root  is  the  apex  and  the  crown,  the  base. 
Therefore  toward  the  apex  of  the  root  is  npward,  and  toward  the  crown 
is  downward,  whether  the  tooth  is  in  the  upper  or  lower  jaw. 


THE   PERIDENTAL  MEMBRANE.  73 

or  occupying  the  apical  space  fig.  36  e  ;  the  body  of  the 
membrane,  which  fills  the  alveolus  from  the  apical  space 
to  the  lower  border  or  rim  of  the  alveolar  wall  a;  and  the 
cervical  or  gingival  portion,  or  that  portion  immediately 
surrounding  the  neck  of  the  tooth  below  the  rim  g. 

The  thickness  of  the  membrane  varies  very  much  in 
different  individuals,  and  in  different  teeth  in  the  same 
individual.  It  is  thickest  in  the  child,  and  it  becomes 
thinner  (normally)  as  age  advances  until  forty,  or  per- 
haps sixty  years  has  been  reached.  In  fig.  37,  I  give  a 
very  accurate  outline  of  a  cross  section  of  the  alveolus 
with  its  contents  from  a  lamb  (temporary  tooth),  cut  at 
about  the  middle  of  the  lower  third  of  the  body  of  the 
membrane ;  and  in  fig.  38,  another  from  the  cuspid  tooth 
of  a  man  forty  years  old,  cut  a  little  closer  to  the  gingival 
border,  so  as  to  include  the  thickened  rim  of  the  alveolar 
wall.  These  are  drawn  as  enlarged  by  a  two-inch  lens 
(using  a  camera  lucida),  and  then  reduced  one-half,  and 
illustrate  very  fairly  the  extremes  which  occur,  normally, 
in  the  thickness  of  this  membrane.  Such  blood-vessels 
as  could  be  clearly  seen  with  this  low  power  are  shown 
in  their  proper  positions  and  dimensions.  It  will  be  seen 
that  these  are  usually  midway  between  the  alveolar  wall 
and  cementum,  in  the  central  part  of  the  membrane,  in 
the  young  subject ;  while  in  the  old  they  are  more  gene- 
rally close  to  the  bone,  indeed  very  many  of  them  lie  in 
grooves  in  the  alveolar  wall. 

The  direction  of  the  fibers  of  the  membrane  in  the 
position  of  the  sections  is  indicated  as  perfectly  as  is  prac- 
ticable with  this  low  power  of  the  microscope.  Variations 
in  the  thickness  of  the  membrane  are  presented  in  its 
different  parts,  but  these  seem  to  follow  no  rule  whatever, 
except  that  it  may  be  that  the  apical  portion  is  generally 
somewhat  thicker  in  young  subjects.  With  this  exception, 
the  differences  in  thickness  seem  to  be  mere  irregularities 
in  the  contour  of  the  alveolus,  which  is  constantly  under- 
10 


74  THE   PEEIDENTAL  MEMBRANE. 

going  change  by  absorption  and  rebuilding  of  bone.  The 
general  form  of  the  membrane  is  better  seen  in  fig.  36 
from  a  lengthwise  section  of  an  incisor  tooth  of  a  young 
kitten.  This  tooth,  though  very  slender,  is  so  small  (only 
three-sixteenths  of  an  inch  long)  that  it  gives  a  better 
opportunity  for  a  full  length  illustration  than  the  larger 
teeth  of  man.  The  elements  of  the  membrane  are  the 
same,  however,  both  in  form  and  arrangement  in  relation 
to  the  root  of  the  tooth  and  its  alveolus.  My  principal 
object  in  presenting  this  illustration  has  been  to  give  a 
correct  outline  picture,  including  the  entire  root  with  its 
alveolar  walls,  in  which  the  direction  of  the  fibers  should 
be  correctly  indicated  in  all  of  its  parts.  For  this  pur- 
pose I  have  selected  a  section  in  which  the  fewest  number 
of  blood-vessels  appeared,  and  in  which  there  is,  there- 
fore, the  least  distortion  of  the  fibrous  arrangement.  On 
the  lingual  side,  there  is  some  modification  of  the  form 
of  the  alveolus  occasioned  by  the  nearness  of  the  crypt 
of  the  permanent  tooth,  a  portion  of  the  sacculus  of 
which  is  seen  at  m.  This  has  caused  the  thickness  of 
the  membrane  to  be  diminished  in  its  neighborhood. 
Farther  toward  the  crown,  and  also  toward  the  apex  of 
the  root,  the  membrane  is  thicker.  A  close  study  of  the 
illustration,  with  the  aid  of  the  description  accompanying 
it,  will  give  a  good  idea  of  the  general  form  and  arrange- 
ment of  the  membrane. 

THE  PRINCIPAL  FIBERS   OF  THE  MEMBRANE. 

Those  fibers  which  are  fixed  in  the  cementum  and 
from  thence  stretch  across,  and  are  fixed  in  the  alveolar 
wall,  or  into  some  other  tissue,  as  the  fibrous  mass  of  the 
gums,  and  thus  serve  to  maintain  the  tooth  in  its  position, 
I  shall  term  the  principal  fibers  of  the  peridental  mem- 
brane. These  are  of  first  importance  in  the  study  of  this 
membrane,  for  with  the  exception  of  some  deviations  from 
the  usual  course  of  these  for  the  accommodation  of  the 


THE  PER1DENTAL  MEMBRANE.  76 

blood-vessels  and  nerves,  the  other  elements  are  so  dis- 
posed as  not  to  interfere  materially  with  their  arrange- 
ment. The  structure  is  at  the  same  time  so  very  complex 
that  we  need  to  bring  to  our  aid  every  available  device 
for  gaining  a  clear  comprehension  of  the  arrangement  of 
its  elements.  To  this  end  the  arrangement  of  the  prin- 
cipal fibers  should  be  first  studied,  and  afterwards  the 
character  of  the  fibers  themselves,  and  following  this  the 
inter-fibrous  elements. 

ARRANGEMENT   OP  THE  FIBERS. 

Beginning  with  the  gingival  portion,  we  find  the  prin- 
cipal fibers  firmly  fixed  to  the  cementum,  literally  spring- 
ing out  of  it,  and  passing  diractly  out,  or  but  slightly 
divergent,  from  all  the  surfaces  of  this  part  of  the  tooth. 
The  manner  of  the  fixation  of  these  fibers  in  the  cementum 
will  be  studied  in  detail  later. 

On  passing  out  from  the  cementum  they  may  retain 
the  solid  form  (fig.  39)  or  split  up  into  fasciculi  of  finer 
fibers  (fig.  42).  In  the  latter  case,  which  is  the  more 
common,  they  show  some  disposition,  in  many  localities, 
to  gather  into  loose  bundles,  the  elements  of  which  pur- 
sue a  common  course.  But  more  generally  perhaps  the 
bulk  of  the  fibers  lie  parallel  with  each  other,  deviating 
only  to  give  place  to  blood-vessels  and  nerves,  or  the 
larger  groups  of  lymphatics.  Upon  the  labial  and  lingual 
surfaces  of  incisors  these,  after  passing  out  some  little 
distance  from  the  tooth,  are  lost  in  the  coarse,  tangled, 
fibrous  tissue  of  the  gums.  This  is  fairly  well  seen  in 
figs.  36  and  40,  g.  g.  Usually  there  is  a  fairly  strong 
fibrous  bundle  turning  down  into  the  gingivus  (fig.  36,  7i), 
especially  on  the  labial  side.  Nearer  the  border  of  the 
alveolar  wall  the  fibers  pass  on  under  the  gum  tissue 
proper,  and  are  continuous  with  the  outer  layer  of  the 
periosteum  of  the  outer  surface  of  the  alveolar  walls.  As 
these  pass  the  margin  of  the  alveolus,  fibers,  springing 


76  THE   PERIDENTAL   MEMBRANE. 

out  of  the  bone,  first  decussate  with,  and  then  become 
mingled  with  them,  thus  forming  a  very  firm  support  to 
the  gingivus.  This  bundle  has  been  termed  the  dental 
ligament. 

As  we  pass  around  the  teeth  toward  the  lateral  sur- 
faces a  disposition  of  the  fibers  to  bend  away  laterally  is 
noticed  (fig.  40),  and  before  we  have  fully  reached  the 
lateral  surfaces  the  fibers  may  be  traced  continuously  to 
the  neighboring  tooth,  following  a  somewhat  curved 
course,  and  passing  the  lower  margin  of  the  alveolar  wall. 
Between  neighboring  teeth  the  fibers  pass  directly,  or  at 
a  slight  inclination  from  one  tooth  to  the  other,  being 
fixed  into  the  cementum  of  each  (fig.  40, /).  In  the  cen- 
tral part  of  their  course  many  blood-vessels  are  seen,  which 
cause  more  or  less  deflection  in  the  course  of  individual 
bundles  of  fibers.  If  the  horizontal  section,  including  two 
teeth,  is  cut  very  close  to  the  margin  of  the  alveolar  walls 
the  fibers  will  be  found  to  break  up  into  bundles  near  the  ' 
central  portion,  and  many  of  them  pass  out  of  the  section, 
while  a  portion  continue  on  from  tooth  to  tooth.  The 
arrangement  of  the  fibers  on  the  lingual  side  does  not 
differ  materially  from  that  of  the  labial  as  shown  in 
fig.  40. 

The  gingivus,  or  free  border  of  the  gum  (fig.  36,  A)  is 
covered  with  a  moderately  thick  but  very  dense  epithelial 
coating,  surmounted  upon  the  fibers  emanating  from  the 
cementum  of  the  neck  of  the  tooth  and  the  dense  tangled 
mass  of  fibrous  tissue  forming  the  gums.  Considerable 
importance  has  been  given  to  that  portion  of  the  epithe- 
lium of  the  gingivus  lying  next  to  the  neck  of  the  tooth, 
which  is  composed  of  softer  and  more  delicate  cells  than 
other  portions.  I  will  return  to  this  point  later. 

The  fibers  of  the  lower  portion  of  the  body  of  the 
membrane  run  nearly  directly  across  from  the  cementum 
to  the  walls  of  the  alveolus,  which  they  enter.  Those 
entering  at  the  rim  of  the  alveolus  usually  have  an  incli- 


THE  PERIDENTAL  MEMBRANE.  77 

nation  upward  (toward  the  root  of  the  tooth)  as  shown 
in  the  illustration,  but  a  little  farther  upward  they  ruu 
squarely  across,  following  nealy  a  straight  course.  It  is 
here  that  the  largest  and  strongest  fibers  of  the  peridental 
membrane  are  found,  and  we  can  often  trace  individual 
fibers  entirely  across  from  the  cementum  to  the  bone, 
even  in  young  subjects,  both  in  lengthwise  and  cross  sec- 
tions. It  is  the  region  from  which  the  sections  for  figs. 
37  and  38  were  taken.  As  we  pass  farther  toward  the 
apex  of  the  root  the  trend  of  the  fibers  in  passing  from  the 
cementum  to  the  alveolar  wall  becomes  more  and  more 
downward  (toward  the  crown),  and  at  the  same  time 
a  greater  disposition  to  form  into  fasciculi  or  loose  bun- 
dles is  noted.  In  young  subjects,  when  the  membrane  is 
thick,  some  of  these  bundles  are  very  long,  reaching  for  a 
considerable  distance  along  the  root  to  be  attached 
finally  to  the  alveolar  wall.  This  disposition  to  form  into 
fasciculi  is  seen  most  prominently  perhaps,  well  up 
toward  the  apex  of  the  root,  where  a  greater  portion  of 
the  alveolus  is  occupied  by  different  tissues.  Here  fan- 
like  fasciculi  radiating  from  the  cementum  bone  quite 
common,  standing  out  as  broad  bands  of  fibers  pursuing  a 
straight  course  from  the  cementum  to  the  bone,  as  if  put 
upon  the  stretch  ;  as  shown  on  the  lingual  side  near  the 
end  of  the  root  of  the  tooth  in  fig.  36. 

Finally  in  the  apical  space  (fig.  36,  e)  the  disposition 
of  the  fibers  is  extremely  irregular.  Indeed  in  young 
subjects  the  tissue  here  has  often  more  the  appearance  of 
embryonic  tissue,  in  which  there  are  few  fibers  developed, 
except  those  accompanying  the  blood-vessels,  which  lat- 
ter are  large  and  often  divide  into  a  number  of  branches, 
some  entering  the  apical  foram  to  supply  the  pulp  of  the 
tooth,  and  others  passing  down  in  the  peridental  mem- 
brane. In  older  subjects  fibers  are  developed  here  which 
pass  pretty  directly  from  the  root  to  the  bone  in  radiating 
fasciculi. 


78  THE  PERIDENTAL   MEMBRANE. 

This  is  in  brief  the  arrangement  of  the  principal  fibers 
of  the  membrane,  as  seen  in  well  prepared  sections.    How- 
ever, many  sections,  when  large  numbers  are  examined, 
will  come  under  the  lens,  which  show  wide  variations 
from  this  arrangement.     First,  if  the  lengthwise  section 
is  cut  a  little   to  one  side  of  the  center,  perhaps  very 
few  fibers  will  appear ;  or  one  not  well  skilled  in  the 
examination  will  fail  to  make  them  out  as  they  lie  among 
the  cellular  elements,  for  the  reason  that  they  are  cut 
across  at  more  or  less  of  an  angle.     Especially  will  this  be 
the  case  if  the  section  is  mounted  plain  in  glycerine,  or  if 
it  be  well  stained  with  a  good  nucleus-tinting  dye.     In 
either  case  the  cellular  elements  will  be  rendered  prom- 
inent, and  the  fibers,  which  remain  transparent,  will  be 
hidden  from  view.     I  have  many  sections  in  which  no 
fibers  could  be  made  out,  but  from  the  fact  that  they  are 
so  thick  that  the  cells  of  the  inter-fibrous  tissue,  which  lie 
between  them,  appear  in  rows  (fig.  41).     Those  prepared 
in  the  same  manner,  but  which  are  a  little  thicker,  so  that 
the  cells  lie  upon  the  fibers  as  well,  show  no  appearance 
of  fibers  whatever.     The  same  class  of  sections,  however, 
stained  diffusely  with  carmine,  or  pigmented,  show  the 
fibers  prominently.     Secondly,  many  lengthwise  sections 
follow  blood-vessels  which  traverse  the  membrane  in  this 
direction.     These  often  are  surrounded  by  more  or  less 
indifferent  fibrous  tissue.    These  fibers  may  lie  parallel  to 
the  course  of  the  vessels,  and  it  is  manifest  that  where 
the  line  of  one  of  these  happens  to  be  followed,  the  mem- 
brane will  appear,  or  rather  will  actually  be  divided  into 
two  parts,  one  of  which  will  be  attached  to  the  cemen- 
tum,  and  the  other  to  the  alveolar  wall.     It  will  be  seen 
at  once  that  unless  the  elements  seen  are  well  understood, 
a  very  erroneous  conclusion  may  be  arrived  at,  that  of  a 
double  membrane.     One  would  suppose  from  reading  our 
literature  that  such  had  actually  been  the  case. 

With  increasing  age  the  cementum  is  thickened,  the 


THE  PERIDENTAL  MEMBRANE.  79 

walls  of  the  alveolus  are  strengthened,  the  thickness  of 
the  peridental  membrane  diminished,  and  all  its  fibers 
shortened  by  being  included  in  the  cementum  on  the  one 
side,  and  in  the  bone  on  the  other.  In  this  case  the  fibers 
generally  appear  to  pass  more  directly  from  the  cemen- 
tum to  the  bone  in  all  of  the  upper  portion  of  the  alveolus; 
yet  the  general  trend,  as  illustrated  in  fig.  36,  is  fairly 
maintained. 

If  this  arrangement  of  the  fibers  be  studied  with  ref- 
erence to  the  physical  functions  of  the  membrane — i.  e., 
that  of  maintaining  the  tooth  in  its  position  during  the 
strain  of  its  normal  usage,  it  will  be  found  that  it  is  the 
very  best  that  could  be  devised  for  the  purpose.  The 
tooth  is  swung  in  its  socket  in  such  a  manner  as  best  to 
resist  a  strain  upward  upon  its  crown,  and  save  the  tissues 
of  the  apical  space  from  injury,  while  the  fibers  running 
squarely  across  in  the  lower  third  of  the  body  of  the  mem- 
brane prevent  displacement  laterally. 

The  fibers  of  the  peridental  membrane  are  wholly  of 
the  white  or  inelastic  connective  tissue  variety.  There 
are  no  elastic  fibers,  or,  at  least,  I  have  not  been  able  to 
find  any  remaining  after  dissolving  out  the  white  fibers 
with  alkaline  solutions.  The  form  of  the  principal  fibers, 
though  in  many  respects  bearing  a  close  conformity  to  the 
fibers  of  the  internal  layer  of  the  attached  periosteum  is 
peculiar  to  this  membrane.  Indeed,  in  many  localities 
no  difference  could  be  observed,  if  the  examination  were 
confined  to  the  immediate  surface  qf  the  alveolar  process. 
The  fibers  of  this  portion  are,  however,  in  the  main  larger 
than  those  of  the  periosteum  and  rather  less  thickly 
placed.  While  in  many  localities  they  break  up  into  fine 
fibers  almost  immediately  after  passing  out  of  the  bone, 
as  is  the  case  in  the  inner  layer  of  the  attached  periosteum, 
in  others  they  continue  far  out  into  the  membrance  as 
strong,  seemingly,  solid  cords,  with  perhaps  finer  fibers 
and  cellular  elements  running  in  a  different  direction, 


80  THE   PERIDENTAL   MEMBRANE. 

interwoven  between  them  (fig.  46).  In  thin  sections  cut 
parallel  with  the  fibers  and  stained  with  a  good  nucleus- 
tinting  dye  this  arrangement  gives  the  tissue  a  very  char- 
acteristic appearance.  The  fibers  are,  in  this  case,  per- 
fectly transparent  and  invisible,  and  the  cellular  elements, 
which  lie  between  them,  appear  disposed  in  rows  as  shown 
in  fig.  41.  Sections  from  the  same  series  diffusely  stained, 
or  pigmented,  show  the  fibers  prominently. 

The  appearance  of  the  fibers  varies  very  much  in  dif- 
ferent cases,  and  even  in  the  same  case  in  different  modes 
of  preparation  and  staining.  For  instance,  fibers  that 
appear  as  solid  cords  when  stained  with  hematoxylin,  may 
appear  as  fasciculi  composed  of  very  fine  fibers,  when 
stained  diffusively  with  carmine.  By  this  means  we  learn 
that  the  most  compact  of  these  coarser  fibers  are  really 
condensed  bundles  of  fine  connective  tissue  fibers.  In 
the  peridental  membrane  these,  the  individual  fibers,  are 
often  as  compact  as  any  that  I  have  seen  from  the  strong- 
est tendons,  but  these  coarser  fibers  are  not  themselves 
gathered  into  bundles  as  in  the  tendons.  Hence  the 
fibrous  arrangement  here  is  not  similar  to  that  of  a  tendon 
or  ligament.  While  the  fibers  in  many  localities,  espe- 
cially next  to  the  bone,  are  large  and  strong,  each  one 
stands  somewhat  apart  from  its  neighbors  with  other  ele- 
ments intervening,  which  is  not  the  case  in  the  tendon  or 
ligament.  Therefore  while  the  passive  function  of  this 
membrane  is  that  of  fixation  of  the  tooth  in  its  position 
and  of  the  same  nature  as  that  of  a  ligament,  it  has  not 
in  any  of  its  parts  the  structure  of  a  ligament. 

The  fibers  passing  out  from  the  cementum  are  some- 
what smaller  and  more  thickly  placed  than  those  spring- 
ing from  the  alveolar  wall,  but  otherwise  have  the  same 
character.  In  young  subjects  the  parallel  arrangement  of 
these  is  somewhat  interrupted  near  the  cementum  by  the 
lymphatics  which  lie  between  them  in  great  abundance. 
These  fibers  springing  from  the  cementum  on  the  one 


THE  PERIDENTAL  MEMBRANE.  81 

hand  and  from  the  bone  forming  the  walls  of  the  alveolus 
on  the  other,  stretch  across  the  intervening  space  in  the 
directions  indicated  in  fig.  36,  but  there  is  something  more 
in  the  arrangement.  While  in  some  cases  individual 
fibers  are  maintained  as  such,  and  can  be  traced  from  side 
to  side,  as  shown  in  fig.  39,  the  rule  is  that  the  larger 
fibers  springing  from  either  source  break  up  into  fasciculi 
of  very  fine  fibers  as  shown  in  fig.  42,  and  their  individu- 
ality is  lost  by  commingling  with  others.  The  fasciculi 
are,  however,  continuous  from  the  bone  to  the  cementum. 
The  central  part  of  the  membrane  therefore  seems,  and  is 
actually  composed  of  finer  fibers  than  either  its  cemental 
or  osteal  margin.  The  fibers  springing  from  the  cemen- 
tum very  generally  break  up  into  fasciculi  almost  im- 
mediately. It  is  only  near  the  cervical  border  of  the 
membrane  or  opposite  the  rim  of  the  alveolus  that  we  see 
them  generally  continuing  as  solid  fibers  for  any  consid- 
erable distance.  However  occasional  fibers,  or  a  few 
together  may  be  found  here  and  there  in  any  portion  of  it 
which  do  continue  from  side  to  side,  especially  near  the 
apex  of  the  root  where  there  are"  often  found  individu- 
alized groups  of  such.  Those  arising  from  the  bone  and 
especially  those  near  the  rim  of  the  alveolus  often  con- 
tinue as  solid  fibers  through  one-third  or  even  one-half 
the  thickness  of  the  membrane,  giving  off  only  occasional 
small  fibers,  but  near  the  central  part  they  generally  break 
up  into  fasciculi  and  their  identity  is  lost. 

In  the  thick  membranes  of  young  subjects  there  is 
usually  a  very  distinct  vascular  region  near  the  central 
portion,  or  midway  between  the  bone  and  the  cementum. 
It  is  in  this  region  or  zone  that  the  principal  blood-vessels 
and  nerve-trunks  are  found.  This  causes  much  irregu- 
larity in  the  course  of  the  fibers  of  this  region,  for  the 
fasciculi  are  deflected  from  their  course  in  passing  the 
vessels.  Besides  these  deflections  we  often  find  consider- 
able bundles  of  fibers,  especially  in  the  middle  portion, 


82  THE   PERIDENTAL   MEMBRANE. 

or  high  up  on  the  root,  pursuing  a  course  very  different 
from  the  general  trend,  and  these  pass  between  the  fas- 
ciculi and  have  the  effect  of  modifying  their  course.  In 
cross  sections  of  the  contents  of  the  alveolus  these  are 
seen  cut  across. 

As  age  advances  the  appearance  of  the  tissues  of  the 
membrane  is  considerably  changed.  Most  of  the  cellular 
elements  disappear,  and  the  fibers  appear  more  promi- 
nently. These  latter  are  very  much  shorter,  and  it  is 
easier  to  follow  them  through  from  the  cementum  to  the 
bone.  In  many  regions  there  is  no  appearance  of  inter- 
fibrous  tissue  whatever,  and  fasciculi  or  bands  of  fibers 
cut  parallel  to  their  length  often  appear  prominently.  In 
fig.  39, 1  have  represented  such  a  band  of  fibers  seen  pass- 
ing from  the  cementum  a,  to  the  alveolar  wall  b.  The 
illustration  is  taken  from  a  perpendicular  section  of  the 
roots  and  alveolus  of  a  first  molar  of  a  man  seventy  years 
old.  The  fibers  of  the  lower  portion  of  the  figure  c,  pass 
entirely  through  the  membrane  without  breaking  up  into 
fasciculi.  This  occurs  only  occasionally  in  rather  small 
bands  of  fibers  lying  parallel  or  nearty  so.  The  more 
general  form  of  the  fibers  is  that  represented  at  d,  in  the 
same  figure  where  they  break  up  into  fine  fibers  soon  after 
leaving  the  cementum,  as  in  figs.  42  and  43.  In  passing 
the  sections  about  under  the  lens,  bringing  different  por- 
tions of  the  membrane  successively  into  view,  a  great  va- 
riety of  appearances  will  be  noted.  Wherever  the  section 
is  parallel  with  the  length  of  the  fibers  they  will  be  seen 
emerging  from  the  bone  and  cementum,  and  generally 
breaking  up,  as  shown  in  fig.  42,  into  fasciculi  that  then 
pursue  a  wavy  course,-  usually  more  or  less  obliquely 
toward  the  other  side.  Not  very  infrequently  strong 
groups  will  be  found  arising  from  either  bone  or  cemen- 
tum that  spread  out  fan-like,  as  seen  in  fig.  43,  some  of 
which  may  be  traced  through  the  membrane  while  others 
pass  out  of  the  section  or  are  lost  by  mingling  with  other 


THE   PERIDENTAL   MEMBRANE.  83 

fibers.  In  rambling  over  the  membrane  with  the  micro- 
scope many  points  are  found  at  which  there  appears  to  be 
no  attachment  whatever.  This  in  many  instances,  is 
from  the  fact  that  the  section  is  not  parallel  with  the 
fibers  at  that  point,  which  can  often  be  definitely  made 
out  by  the  presence  of  fibers  cut  obliquely.  But  at  other 
points,  and  these  are  not  few,  certainly  no  attachment  has 
existed.  Indeed  the  principal  fibers  may  be  absent  and 
the  fibers  of  the  indifferent  tissue  may  lie  flat  upon  the 
surface  of  the  cementum  or  bone  for  a  considerable  space. 
Their  course  being  parallel  with  the  surface.  At  some 
points  the  cause  of  the  detachment  is  evidently  absorp- 
tions of  the  alveolar  wall  or  of  the  surface  of  the  cemen- 
tum, and  the  principal  fibers  may  be  seen  to  have  been 
severed.  The  osteoclasts  are  found  frequently,  and  the 
roughened  surface  tells  plainly  of  their  action,  even  at 
this  advanced  age.  It  has  become  plain  to  me  after  a  long 
study  of  this  point  that  the  attachment  of  the  fibers  is 
continually  changing.  They  seem  to  be  loosened  and 
remain  so  for  a  time,  but  they  are  again  attached,  or  new 
fibers  are  developed.  Some  other  part  is  loosened  and 
again  attached,  so  that  in  passing  around  the  root  of  a 
tooth  of  an  old  person  these  non-attached  points  are  con- 
tinually coming  into  view.  This  will  be  studied  more  in 
detail  under  absorptions  within  the  alveolus. 

As  has  been  said,  the  interfibrous  tissue  is  much  di- 
minished in  old  age.  At  many  points  none  whatever  can 
be  seen ;  at  some  points,  however,  there  is  so  much  of  this 
that  it  might  be  mistaken  for  a  young  membrane.  In  run- 
ning along  the  surface  of  the  cementum  occasional  groups 
of  cementoblasts  appear  with  undeveloped  cells  in  their 
neighborhood.  The  same  appearances  of  local  activity 
are  met  with  along  the  bony  wall  also. 


CHAPTER  IX. 

INTER-FIBROUS  ELEMENTS    OP   THE   PERIDENTAL 
MEMBRANE. 

Other  than  the  blood-vessels  and  nerves,  the  principal 
interfibrous  elements  are  an  indifferent  tissue,  and  the 
various  forms  of  cells.  The  principal  fibers  are  accom- 
panied by  fibroblasts,  which  belong  to  them,  and  are  ren- 
dered prominent  by  any  nucleus-tinting  dye.  Fig.  50,  D. 
But  aside  from  these  there  is  among  the  principal  fibers 
a  very  considerable  number  of  fibroblasts,  accompanied 
by  very  fine  fibers,  which  pass  between  the  principal 
fibers  and  often  pursue  an  independent  direction.  Fig. 
46.  This  I  have  termed  the  interfibrous  or  indifferent 
tissue.  It  seems  to  pervade  the  entire  membrane,  and 
is  found  wherever  the  principal  fibers  are  absent,  or  are 
coarse  enough  for  it  to  be  distinguished.  In  figure  46  I 
have  represented  this  tissue  with  a  high  power.  The 
illustration  is  taken  from  the  margin  of  bone  near  the  rim 
of  the  alveolus,  where  the  principal  fibers  are  very  large. 
The  interfibrous  tissue  is  seen  to  be  ordinary  fibrous  con- 
nective tissue  containing  the  usual  fibroblasts.  In  this 
instance  its  course  is  diagonal  to  the  principal  fibers. 
This  tissue  is  well  seen  in  many  regions  of  the  membrane, 
but  when  it  is  mingled  with  the  principal  fibers  of  the 
vascular  region  its  identity  is  necessarily  lost,  except 
where  it  forms  an  investment  for  the  vessels  and  nerves. 
Fig.  50,  E  and  F.  Parts  of  the  membrane  here  and  there 
are  made  up  seemingly  of  this  tissue,  the  principal  fibers 
being  absent.  Fig.  49  d.  This  is  most  frequently  seen 
high  up  on  the  root  or  about  its  apex,  and  marks  espe- 
cially those  regions  of  the  membrane  that  I  havedesignat- 

84 


INTER-FIBROUS   ELEMENTS.  85 

ed  in  previous  pages  as  non-attached.  In  general,  when 
standing  alone,  it  gives  the  appearance  of  indifferent  tis- 
sue. In  the  young  subject  its  fibroblasts  are  a  marked 
feature  of  the  membrane  when  stained  with  a  good 
nucleus-tinting  dye,  but  in  the  old  these  become  very  thin 
scales,  and  do  not  take  stains  well,  so  that  it  is  difficult 
to  distinguish  them  except  with  high  powers.  The  tissue 
then  appears  loosely  fibrous,  and  the  fibers,  while  pursu- 
ing no  very  definite  direction,  have  a  general  tendency  to 
lie  horizontally  to  the  cementum,  or  parallel  with  its 
margin,  as  seen  in  lengthwise  sections.  It  does  not  seem 
to  attach  itself  to  the  cementum  or  bone,  as  do  the  prin- 
cipal fibers.  The  fibrous  investment  of  the  blood-vessels 
and  nerves,  additional  to  the  tissue  properly  belonging  to 
their  walls,  seems  to  belong  to  this  tissue.  In  young  sub- 
jects this  is  often  very  abundant  (fig.  50,  E  and  F),  form- 
ing masses  accompanying  the  vessels,  and  causing  devia- 
tions in  the  course  of  the  principal  fibers.  In  older  sub- 
jects this  accompaniment  of  the  blood-vessels  mostly  dis- 
appears, and  in  sections  their  walls  look  comparatively 
thin. 

BLOOD    SUPPLY   OF   THE   PERIDENTAL   MEMBRANE. 

The  blood  supply  of  the  peridental  membrane  is  very 
bountiful  in  the  young  subject,  and  though  it  is  much 
diminished  with  the  thinning  of  the  membrane  as  age  ad- 
vances the  vessels  remain  fairly  abundant.  In  the  young 
subject  there  is  a  very  well  marked  vascular  area  lying 
centrally  between  the  cementum  and  alveolar  wall,  or 
often  rather  closer  to  the  cementum.  This  is  most  reg- 
ularly seen  in  cross  sections.  Through  this  portion  the 
fibers  are  deflected  from  their  regular  course  in  many 
parts  to  give  space  to  the  larger  arteries,  veins  and  nerve 
bundles.  Fig.  50,  E.  and  F.  The  larger  arteries  enter 
the  alveolus  mostly  at  the  apical  space,  or  rather  one  or 
two  ve'ssels  enter  here,  and  immediately  break  up  into 


86  INTER-FIBROUS    ELEMENTS. 

smaller  ones.  One  or  two  of  these  enter  the  root  canal 
to  supply  the  pulp  of  the  tooth,  while  the  others — from 
four  tq  six  or  eight — pass  down  along  the  sides  of  the 
root  to  supply  the  peridental  membrane.  In  their  passage 
down  the  membrane  these  divide  into  many  branches,  a 
considerable  number  of  which  enter  the  Haversian  canals 
of  the  alveolar  wall,  or  receive  branches  from  that  source. 
This  kind  of  connection  between  the  circulation  of  the 
tissues  outside  of  the  alveolar  wall  and  the  peridental 
membrane  is  very  rich  in  young  subjects,  and  although 
the  bone  becomes  much  more  dense  with  advancing  age 
it  is  still  fairly  well  maintained.  Seemingly  for  this  reason 
there  is  not  much  diminution  in  the  size  of  the  main 
arteries  passing  down  from  the  apical  space  to  the  gin- 
givus,  though  they  are  much  increased  in  numbers.  We 
may  therefore  say  very  justly  that  the  blood  supply  of 
this  membrane  is  received  largely  through  the  walls  of 
the  alveolus.  Some  vessels  are  continuous,  however,  from 
the  apical  space  to  the  gingivus.  I  have  a  few  sections 
from  the  incisor  teeth  of  the  dog  cut  lengthwise,  inject- 
ed, that  show  arteries  traversing  the  membrane  from 
apex  to  gingivus  without  break,  but  giving  off  and  receiv- 
ing branches  from  the  alveolar  wall  throughout  their 
course.  Many  of  these  branches  can  be  traced  through 
the  alveolar  wall  to  their  connection  with  the  larger  ves- 
sels of  the  gum-tissue.  These  vessels  during  their  course 
in  the  peridental  membrane  give  origin  to  a  fairly  rich 
capillary  plexus  that  supplies  its  tissues.  It  is  rare  to  see 
a  vessel  of  any  size  close  to  the  cementum.  This  portion 
of  the  tissue  seems  to  be  supplied  almost  solely,  but  very 
richly,  by  the  smaller  capillaries.  The  passing  and  re- 
passing  of  the  vessels  through  the  alveolar  wall  is  well 
seen  in  sections,  and  shows  many  of  the  larger  ones  near 
the  bone  and  within  its  canals.  With  the  thinning  of  the 
membrane  as  age  advances  the  vessels  are  found  lying 
very  close  to  the  bone,  and  in  case  the  membrane  is  very 


INTER-FIBROUS    ELEMENTS.  87 

thin  many  of  them  lie  in  grooves  in  the  bone.  This  is 
best  seen  in  cross  sections.  (Fig.  37.)  Veins  accompany, 
or  perhaps  stand  a  little  apart  from,  most  of  the  larger 
arteries.  At  the  rim  of  the  alveolus  the  vessels  of  the 
peridental  membrane  anastomose  very  freely  with  those 
of  the  gum,  and  this  gives  a  pretty  rich  gingival  plexus. 

From  this  arrangement  of  the  circulation  of  the  blood 
in  this  membrane  it  will  be  seen  that  it  is  not  readily 
robbed  of  its  blood  supply  by  accident.  In  case  of  alve- 
olar abscess  involving  the  apical  space,  the  blood  supply 
from  that  source  is  cut  off,  but  that  through  the  alveolar 
wall  and  by  way  of  the  rim  of  the  alveolus  is  ample ;  or 
even  in  case  the  supply  from  both  the  apical  space  and  by 
way  of  the  rim  of  the  alveolus  is  cut  off  simultaneously, 
the  remaining  body  of  the  membrane  will  be  supplied 
through  the  alveolar  wall,  and  will  not  suffer  from  want 
of  blood.  An  inflammation  involving  one  part  does  not 
necessarily  endanger  another. 

The  sensory  function  of  the  peridental  membrane  is 
supplied  by  nerves  entering  it  in  company  with  the  blood- 
vessels, and  from  all  the  sources  of  blood  supply  men- 
tioned under  that  head.  The  principal  bundles,  how- 
ever, enter  by  way  of  the  apical  space,  and  then  divide, 
a  portion  entering  the  apical  foramen  for  the  supply  of 
the  pulp,  while  the  others  pass  down  the  sides  of  the  root 
supplying  the  peridental  membrane.  A  considerable 
number  enter  through  the  walls  of  the  alveolus  by  way  of 
the  Haversian  canals,  each  containing  from  four  to  ten  or 
more  nerve  fibers.  These  traverse  the  membrane, 
giving  off  smaller  bundles  which  are  lost  in  the  tissue, 
until  the  gingival  border  is  reached,  where,  in  company 
with  those  of  the  gum  tissue,  a  rather  rich  plexus  is 
formed. 

Specialized  nerve  terminations  have  not  been  found  in 
this  membrane  in  sufficient  numbers  to  show  that  they 
are  essential.  I  have  seen  a  few  Pacinian  corpuscles  near 


88  INTER-FIBROUS    ELEMENTS. 

the  gingival  border,  and  rarely  some  other  knob-like 
terminations.  Generally,  however,  none  of  these  are 
found.  The  bundles  of  fibers  sub-divide  into  single  fila- 
ments which  are  lost  in  the  tissues,'  and  probably  termin- 
ate mainly  as  naked  fibers. 

Through  this  supply  of  nerves  the  perrdental  mem- 
brane becomes  the  organ  of  touch  for  the  tooth.  The 
enamel,  the  portion  of  the  tooth  exposed,  has  not  the 
sense  of  touch.  This  may  be  demonstrated  by  experiment 
in  many  ways.  One  of  the  simplest  of  these  is  per- 
formed as  follows :  Take  any  small  instrument  and  touch 
,with  it  the  enamel  of  any  tooth.  It  will  be  found  that 
the  lightest  touch  is  felt  distinctly  by  the  patient.  Now 
place  the  finger  on  the  opposite  side  of  the  tooth  and 
make  firm  pressure,  and  while  this  is  maintained  again 
touch  the  exposed  part  of  the  enamel  with  the  instru- 
ment. It  will  be  found  that  under  these  conditions  the 
touch  will  not  be  felt.  Now  by  varying  the  pressure  with 
the  finger  it  will  be  found  that  in  order  for  the  touch  of 
the  instrument  upon  the  enamel  to  be  felt  it  must  be  suffi- 
cient to  overcome  the  pressure  brought  to  bear  by  the 
finger.  A  slight  movement  of  the  tooth  must  be  pro- 
duced so  that  it  may  effect  the  peridental  membrane, 
without  this  no  sense  of  touch  is  manifested.  This  is 
different  from  the  temporary  semi-paralysis  that  may  be 
produced  by  firm  continued  pressure,  or  by  a  blow.  In 
order  for  this  to  be  effective  it  must  be  pretty  severe  or 
long  continued.  For  comparison  this  may  be  tried  upon 
the  hand  or  fingers.  This  simple  experimentation  readily 
demonstrates  that  the  sense  of  touch  in  the  tooth  is  very 
different  from  that  of  the  skin.  The  sense  of  touch  in  the 
finger  nails  will  be  found  similar  to  that  of  the  tooth. 

Normally,  the  sense  of  pain  is  not  easily  aroused  in  the 
peridental  membrane.  The  office  of  fixation  of  the  tooth, 
and  maintaining  this  against  the  heavy  pressure  normally 
brought  to  bear  upon  it,  demands  the  capability  of  with- 


INTER-FIBROUS    ELEMENTS.  89 

standing  heavy  strain  and  blows  without  complaint,  and 
at  the  same  time  without  limiting,  in  the  absence  of  such 
a  strain,  the  acuteness  of  the  sense  of  touch.  The  mem- 
brane does  not,  however,  on  this  account,  bear  mutilation 
without  pain,  but  is,  perhaps,  as  painful  as  .the  average  of 
the  tissues,  and  in  its  inflamed  state  it  becomes  exceed- 
ingly sensitive  to  very  slight  pressure,  as  is  uniformly 
witnessed  in  acute  pericementitis.  Its  rich  supply  of 
blood-vessels  and  nerves  renders  it  capable  of  rapid 
recovery  from  injuries  of  almost  any  kind.  Indeed,  there 
is  no  tissue  of  the  body  that  shows  a  more  marked  ten- 
dency to  recover  from  severe  injuries. 

These  sensory  functions  are  not  destroyed  by  injury  to 
any  particular  portion  of  the  membrane.  I  have  carefully 
tried  the  sense  of  touch  in  teeth  after  having  removed  all 
of  the  contents  of  the  apical  space,  i.  e.,  after  soreness 
had  so  far  abated  that  the  sense  of  touch  was  not  abol- 
ished by  the  sense  of  pain,  and  found  the  sense  of  touch 
was,  as  far  as  could  be  ascertained,  normal.  That 
its  sensitiveness  to  painful  impressions  is  not  abated 
by  the  destruction  of  the  nerves  entering  by  way  of 
the  apical  space,  is  sufficiently  obvious  to  all  who  have 
had  to  do  with  large  acute  alveolar  abscesses  producing 
extensive  destruction  of  the  tissues  of  the  apical  space. 
It  follows,  therefore,  that  the  nerves  entering  the  mem- 
brane through  the  walls  of  the  alveolus  are  sufficient  for 
the  maintenance  of  the  sensory  functions. 


CHAPTER  X. 

LYMPHATICS   OF   THE  PERIDENTAL   MEMBRANE. 

The  peridental  membrane  has  a  very  peculiar  system 
of  cells  closely  resembling  those  of  the  lymphatics.  In 
young  subjects  these  are  found  in  great  profusion  lying 
among  its  fibers  close  to  the  cementum.  I  know  of  no 
other  system  of  cells  similar  to  this  anywhere  within  the 
bodies  of  men  or  of  the  lower  animals.  They  seem  as 
distinctly  specialized  as  the  agminated  glands  or  Peyer's 
patches  of  the  small  intestine.  I  therefore  regard  them 
as  peculiar  to  this  particular  portion  of  the  peridental 
membrane.  They  occur  mostly  in  the  form  of  rows  of 
cells  insinuated  between  the  fibers  of  the  membrane. 
They  are  never  far  from  the  cementum,  but  not  in  contact 
with  it,  except  in  some  isolated  cases  observed  in  the  pig. 
These  rows  of  cells  anastomose  freely  with  each  other 
and  form  a  network  over  the  whole  of  the  root  of  the 
tooth.  Their  number  is  so  great  that  I  have  counted 
from  one  hundred  to  two  hundred  of  them  cut  across 
in  the  cross  section  of  the  root  and  alveolus  of  an 
incisor  tooth  of  ordinary  size.  Fig.  50,  C,  C.  These 
rows  of  cells  vary  very  much  in  the  numbers  of  cells  in- 
cluded in  their  make-up.  Sometimes  a  cross  section  will 
show  only  one  or  two  cells  lying  together.  Again,  and 
more  commonly,  five  or  six  that  form  a  rounded  group, 
and  more  rarely,  especially  near  the  gingivus,  where  they 
are  generally  larger  and  more  numerous,  there  will  be 
quite  a  body  of  them  giving  with  high  powers  a  gland- 
like  appearance.  I  have  represented  one  of  these  in  fig.  47, 
using  for  the  purpose  the  one-twelfth  inch  objective,  in 
which  its  relations  to  a  small  capillary  vessel  are  shown. 

90 


LYMPHATICS.  91 

Very  often  the  cells  lie  between  the  fibers  in  such  a 
way  as  to  show,  in  cross  or  lengthwise  sections,  rows  run- 
ning outward  from  the  cementum.  This  is  especially  well 
seen  in  the  pig.  These  often  seem  to  be  single  rows  of 
cells,  or  they  may  consist  of  two  or  three  rows  lying 
side  by  side.  In  either  cross  or  lengthwise  sections  the 
islands  of  cells  seem  to  be  entirely  detached  from  each 
other,  especially  if  the  sections  are  very  thin.  But  in  sec- 
tions cut  horizontal  to  the  surface  of  the  cementum  at 
such  a  distance  as  to  include  them,  they  are  seen  to 
be  in  the  form  of  chains  that  anastomose  with  each  other, 
like  a  network.  In  fig.  48  I  have  represented  a  group 
of  these,  using  the  one-eighth  inch  objective.  This 
is  very  readily  seen  with  low  powers  if  the  section,  cut  in 
the  manner  indicated  above,  be  double-stained  with  car- 
mine and  hematoxylin.  In  this  case  the  lymph  cells  take 
the  hematoxylin  and  the  fibrous  tissues  are  stained  red, 
and  with  low  powers,  the  first  impression  will  be  that  of 
a  fine  capillary  injection.  Higher  powers  will  reveal  the 
true  character  of  the  tissue. 

The  individual  cells  are  like  those  of  the  lymphatic 
glands.  They  show  a  circular  or  polygonal  outline,  and 
the  central  portion  takes  the  staining  agent  strongly.  In  the 
larger  groups  it  is  easily  seen  that  they  are  enveloped  in 
a  very  delicate  limiting  membrane.  This  limiting  mem- 
brane is  not  so  easily  seen  about  the  smaller  groups  or 
rows  of  cells.  However,  by  following  one  of  these  carefully* 
which  I  regard  as  a  very  delicate  lymph  duct  crowded  with 
lymphoid  cells,  I  have  been  able  in  many  instances,  to 
connect  it  with  the  smaller  veins  or  capillaries  in  the  form 
of  the  perivascular  spaces  peculiar  to  the  lymphatics  of 
other  regions.  Owing  to  the  extreme  difficulty  of  obtain- 
ing nitrate  of  silver  stainings  of  this  membrane,  it  is  spe- 
cially difficult  to  make  out  these  points  quite  satisfactorily. 

Klein  seems  to  have  shown  that  nodes  of  lymph  cells 
develop  within  the  lymph  sacks  or  enlargements  of  the 


92  LYMPHATICS. 

lymph  ducts,  which  he  designates  as  endolymphangeal, 
and  also  outside,  but  in  contact  with  these,  which  he 
terms  perilymphangeal  nodes.  These  are,  however,  en- 
dolymphangeal, as  distinguished  from  the  peiilymphangeal 
glands  or  nodes.  In  fact,  these  seem  to  be  lymph  canals 
that  are  packed  with  lymphoid  cells  rather  than  true  lym- 
phatic glands.  The  cells  are  very  well  seen  in  plain 
glycerine  mountings,  especially  after  acetic  acid,  and  the 
groups  may  readily  be  made  out  with  the  half-inch  object- 
ive, but  as  they  lie  crowded  among  the  other  tissues 
higher  powers  are  necessary  to  differentiate  them. 

These  cells  are  more  abundant  in  the  omnivora  than 
in  other  animals  that  I  have  examined,  and  the  pig  is  an 
especially  good  subject  for  their  study.  They  are  very 
well  seen  in  the  herbivora,  also,  but  seem  not  so  abundant 
in  the  carnivora.  They  seem  to  diminish  in  numbers  as 
age  advances,  though  this  point  has  not  been  studied  suf- 
ficiently. In  one  membrane  from  a  man,  forty  years  old, 
the  number  seems  to  be  much  diminished,  though  groups 
of  them  were  seen  in  almost  every  field.  In  another  from 
a  man  about  seventy,  only  a  few  groups  of  the  cells  were 
found.  It  seems  probable  that  they  disappear,  for 
the  most  part,  with  advancing  age.  In  this  they  agree 
with  specialized  lymphatics  elsewhere,  such  as  Peyer's 
patches  of  the  small  intestine,  and  a  few  that  have  been 
noted  in  other  positions. 

One  circumstance,  aside  from  the  histological  interest, 
has  directed  my  attention  quite  strongly  to  these  cells.  In 
extracting  a  cuspid  tooth  a  large  piece  of  the  anterior  por- 
tion of  the  alveolar  wall  broke  away,  adhering  to  the  root 
of  the  tooth,  and  gave  me  the  opportunity  of  making  sec- 
tions for  the  study  of  its  membrane.  Phagedenic  perice- 
mentitis  was  destroying  the  membranes  of  some  of  the 
other  teeth,  but  about  this  one  no  pockets  were  observ- 
able, though  there  was  some  slight  redness  of  the  gingivus. 
On  microscopic  examination,  I  found  that  some  of  the 


LYMPHATICS.  93 

lymphatics  near  the  gingival  border  of  the  membrane 
were  in  a  state  of  suppuration,  while  some  others  did  not 
take  staining  agents  well.  This  condition  followed  the 
lymph  chains  in  the  direction  of  the  apex  of  the  root  to  a 
distance  that  surprised  me,  considering  the  very  slight 
signs  ot  disease  visible  before  operating,  and  seemed  espe- 
cially confined  to  these  cells.  Examination  of  them  for 
micro-organisms  was  not  thought  of  in  time. 

This  case  hints  quite  strongly  that  these  lymphatics 
are  the  seat  of  this  very  peculiar  affection.  It  seems  that 
it  is  also  these  glands  that  are  first  affected  in  salivation 
with  mercury,  when,  as  physicians  say,  "  the  gums  are 
just  touched,"  and  the  teeth  become  sore,  when  pressed 
together.  Also,  when  the  teeth  become  sore  from  other 
causes  that  may  be  regarded  as  constitutional,  i.  e.,  from 
some  agent  in  the  blood  that  affects  these  glands. 

Formerly,  it  was  suggested  by  Serres,  who  is  quoted 
by  Salter,  that  the  inner  portion  of  the  epithelium — -that 
portion  clothing  the  border  of  the  gingivus  folded  in 
against  the  tooth — acted  the  part  of  a  gland.  This  part 
of  the  epithelium  is  softer  than  other  portions,  and  the 
gland-like  action  noticed  here  under  the  influence 
of  iodide  of  potassium,  mercury,  and  some  other  remedies, 
evidently  led  to  this  conclusion,  which,  from  clinical  ob- 
servation, seemed  to  me  to  be  justified.  (See  American- 
System  of  Dentistry,  vol.  I,  p.  955.)  But  since  I  have 
made  a  more  critical  study  of  these  lymphatics,  it  has  be- 
come clear  that  the  results  were  derived  from  them 
which  had  been  attributed  to  the  inlying  epithelium  of  the 
gingivus.  I  find  the  lymphatics  to  be  larger  and  much  more 
numerous  just  in  that  neighborhood,  and  while  I  have  found 
no  such  thing  as  a  duct  leading  to  the  gingival  aperture,  the 
glands  lie  in  very  close  proximity  to  it.  .  Furthermore,"  a 
portion  of  the  connective  tissue  in  immediate  conjunction 
with  the  tooth  is  not  covered  by  the  epithelium.  In  other 
words,  there  is  no  attachment  of  the  epithelium  to  the 


94  LYMPHATICS. 

root  of  the  tooth.  It  seems  to  be  through  this  space  that 
the  cells — so-called  salivary  corpuscles — found  under  the 
free  border  of  the  gingivus,  pass.  These  may  be  found 
at  any  time  under  the  healthy  gingivus,  and  their  numbers 
are  augmented  with  every  irritation  of  the  membrane. 
Indeed,  close  clinical  examination  makes  it  apparent  that 
there  is  a  slight  secretion  at  this  point  that  is  not  quite 
satisfactorily  explained  even  yet  by  microscopic  study  of 
the  part. 

HARD  FORMATIONS  WITHIN  THE  PERIDENTAL  MEMBRANE. 

There  are  occasionally  found,  in  the  tissues  of  the  peri- 
dental  membrane,  especially  in  elderly  persons,  certain 
hard  formations  that  resemble  the  calcospherites  so  fre- 
quently found  in  the  tissues  of  the  dental  pulp.  I  have 
seen  more  of  these  about  the  roots  of  the  molars  than 
elsewhere,  but  have  also  found  them  along  the  sides  of 
.the  roots  of  the  bicuspids.  Occasionally  I  have  seen 
these  built  into  the  substance  of  the  cementum,  especially 
in  hypertrophies. 

In  fig.  49  I  present  an  illustration  of  one  of  these, 
rather  a  small  one,  from  the  membrane  of  a  bicuspid, 
which  presents  their  usual  appearance  very  fairly.  They 
are  composed  of  concentric  rings  of  lime  salts  united  by  a 
basis  substance  which  appears  identical  with  the  phlebo- 
liths  of  varicose  veins,  and  calcospherites  of  the  dental 
pulp.  They  do  not,  however,  present  exactly  the  same 
features  of  either  of  these.  They  are  much  larger  than 
the  calcospherites  of  the  dental  pulp,  and  the  incremental 
bands  or  layers  are  much  thicker.  Neither  do  they  pre- 
sent the  nodular  forms  composed  of  numbers  bound 
together  in  one  mass,  so  common  to  either  of  the  before- 
mentioned  bodies.  They  are  usually  seen  like  the  one 
in  the  figure,  as  isolated  spherules,  many  of  which  are 
large  enough  to  be  readily  seen  with  the  naked  eye.  In 
several  instances  I  have  seen  two  spherules  united,  but 


LYMPHATICS.  95 

this  is  unusual.  The  larger  ones,  as  they  appear  in  sec- 
tions, after  being  decalcified,  of  course,  usually  show 
cracks  radiating  from  the  center  toward  the  circumfer- 
ence. This  may  have  occurred  in  the  cutting,  though  I 
have  no  means  of  determining  it.  I  only  know  that  the 
smaller  ones  usually  show  nothing  of  this  kind.  In 
several  instances  I  have  seen  cementum  built  upon  the 
larger  ones,  and  fibers  attached,  showing  that  they  may 
become  a  nidus  for  an  irregular  or  nodulated  hypertrophy. 
I  have  also  in  my  collection  hypertrophies  which  show 
these  forms  in  their  substance.  Further  than  this,  I 
know  nothing  of  the  origin  or  significance  of  these  bodies. 
In  the  peridental  membranes  of  old  people  there  is 
a  considerable  number  of  pigment  granules  found.  They 
occur  isolated,  or  in  groups,  oftenest  about  the  walls  of 
the  blood-vessels,  but  also  a  part  from  these.  They  are 
intensely  black,  rather  small,  and  seem  to  be  amorphous. 
They  remind  one  very  much  of  the  pigment  so  generally 
seen  in  lung  tissue.  They  are  not  present  in  the  periden- 
tal membrane  of  3roung  persons.  Nothing  is  certainly 
known  of  their  origin  or  significance.  The  idea  that 
they  arise  from  extravasations  of  blood  might  be  sug- 
gested, but  this  seems  improbable. 


CHAPTER   XI. 

OSTEOBLASTS   AND   ALVEOLAR    WALL. 

The  osteoblasts  of  the  peridental  membrane  are  found 
on  the  inner  surface  of  the  walls  of  the  alveolus  in  abun- 
dance in  young  subjects.  They  lie  on  the  bone  between 
the  principal  fibers  (figs.  45  and  46),  and  there  are  gen- 
erally many  young  cells  in  the  neighborhood,  filling  in 
between  the  fibers  if  they  are  large  and  solid  as  in  fig.  46, 
or  in  the  meshes  of  the  finer  fibers  when  they  break  up 
close  to  the  bone  as  in  fig.  45.  But  in  this  respect  the 
utmost  variety  will  be  found.  Many  localities,  even  in 
young  subjects,  will  be  found  almost  destitute  of  these 
cells,  while  others,  at  only  a  little  distance  perhaps,  will 
be  crowded  with  them.  In  aged  subjects  they  are  gen- 
erally absent,  or  are  represented  only  by  very  thin  flat- 
tened scales,  lying  close  against  the  bone,  that  are  very 
difficult  of  observation.  But  even  in  these  cases  occa- 
sional areas  will  be  found  in  which  the  osteoblasts  appear, 
covering  the  bone  as  in  the  young,  only  less  profusely. 
These  are  undoubtedly  areas  of  activity,  points  at  which 
bone  is  being  built  up  to  accommodate  some  change  in 
the  position  of  the  tooth.  This  will  be  discussed  farther 
under  the  head  of  absorptions  taking  place  in  the  alveolus. 

The  building  of  bone  occurs  on  the  inner  walls  of  the 
alveolar  processes  in  that  growth  which  fits  them  about 
the  roots  of  the  teeth.  These  additions  are  made  in  the 
same  manner  as  subperiosteal  bone  is  built  up  under  the 
attached  periosteum,  to  which  the  reader  is  referred. 
The  peridental  membrane  is  very  thick  in  young  sub- 
jects, and  the  alveolus  correspondingly  wide.  Bone  is 
deposited  upon  the  inner  walls  of  the  alveolar  process  as 

96 


OSTEOBLASTS   AND   ALVEOLAR   WALLS.  97 

the  membrane  is  reduced  in  thickness.  Indeed  after  the 
alveolar  process  is  once  formed  the  subsequent  deposit  of 
bony  matter  is  mostly  on  the  inner  side,  filling  in  the  en- 
larged space  through  which  the  crown  passed  in  the  pro- 
cess of  eruption,  to  conform  it  to  the  root  of  the  tooth. 
In  this  growth  of  bone  new  canals  seem  not  to  be  formed 
by  the  growth  of  processes  which  arch  over,  as  in  sub- 
periosteal  growths.  Nearly  all  the  canals  formed  open 
into  the  alveolus  very  nearly  in  the  direction  pursued  by 
principal  fibers  of  the  peridental  membrane.  (See  Fig. 
36.)  Many  of  these  approach  the  alveolus  so  obliquely 
that  in  cross  sections  such  canals  appear.  In  lengthwise 
sections,  however,  their  true  character  is  sufficiently  ap- 
parent. The  bone  is  therefore  built  up  in  the  first  in- 
stance in  the  same  manner  as  solid  subperiosteal  bone, 
but  with  canals  running  in  the  direction  of  the  growth, 
or  at  an  angle  inclined  to  that  direction.  This  growth  of 
bone  shows  the  residual  fibers  very  plainly  in  many  of  its 
parts,  for  the  fibers  of  the  peridental  membrane  are  in- 
cluded in  this  in  the  same  manner  as  the  fibers  of  the  at- 
tached periosteum.  This  I  have  attempted  to  illustrate  in 
Fig.  51,  from  a  perpendicular  section  through  the  rim  of 
the  alveolar  wall,  choosing  the  extreme  point  of  the 
alveolar  process  —  that  represented  by  ?>,  Fig.  53  on  the 
labial  side  ;  c?,  Fig.  51  represents  the  extreme  point  of  the 
rim  of  the  alveolar  wall.  /, /,  The  subperidental  bone 
which  is  closely  filled  with  residual  fibers  from  the  large 
fibers  of  the  peridental  membrane,  b.  Subperiosteal  bone, 
which  is  usually  small  in  amount,  and  on  the  labial  side, 
is  confined  mostly  to  the  immediate  rim  of  the  alveolar 
wall ;  for.  on  the  labial  side  there  is  more  often  found  ab- 
sorption of  bone,  thinning  the  alveolar  wall  as  it  is  built 
up  on  the  inner  side.  The  Haversian  bone  is  left  without 
stippling  that  it  may  be  more  plainly  marked,  and  is 
pointed  out  by  a.  g,  g,  g,  Are  points  at  which  absorption 
of  bone  is  in  active  progress,  e,  Points  out  the  fibers  of 


98  OSTEOBLASTS   AND   ALVEOLAR   WALLS. 

the  peridental  membrane.  This  bone,  forming  the  alveo- 
lar wall,  it  will  be  seen,  is  first  built  up  solid  as  under  the 
firmly  attached  periosteum.  There  is,  therefore,  no  differ- 
ence in  the  building  of  bone  here  and  elsewhere,  except 
that  the  included  fibers  are  larger,  which  gives  the  bone 
quite  a  characteristic  appearance.  This  bone  is  very  soon 
invaded  by  absorbents,  and  canals  are  burrowed  through 
it,  which  is  followed  by  the  deposit  of  systems  of  Haver- 
sian  bone,  thus  removing  the  fibers,  as  shown  in  the  fig- 
ure. This  process  follows  very  closely  the  building  of 
the  bone,  so  that  there  is  not  at  any  time  a  very  consider- 
able amount  of  the  alveolar  wall  that  shows  residual 
fibers.  This  is  well  shown  in  Fig.  51,  in  which  I  have 
left  the  Haversian  bone  without  stippling  to  distinguish 
it  more  clearly.  At  maturity  the  bone  has  become  so 
changed  by  this  process  that  the  residual  fibers  are  con- 
fined to  the  immediate  surface,  and  almost  the  entire  mass 
of  the  alveolar  wall  is  seen  to  be  made  up  of  secondary 
Haversian  systems.  In  old  subjects  these  show  all  along 
the  inner  border  the  effects  of  absorptions  and  rebuild- 
ings  of  bone  that  have  occurred  from  time  to  time  for  the 
accommodation  of  changes  in  the  positions  of  the  teeth. 
This  matter  will  be  discussed  in  detail  later. 

A  description  of  the  origin  of  the  alveolar  process  be- 
longs rather  to  embryology,  and  I  shall  not  enter  the  dis- 
cussion of  that  part  of  the  subject  here.  The  growth  of 
the  alveolar  process,  after  the  tooth  has  taken  its  place  in 
the  arch,  presents  some  peculiar  features.  This  growth 
is,  in  a  large  degree,  contemporaneous  with  the  develop- 
ment of  the  tooth's  root,  whether  it  be  a  temporary  or 
permanent  tDoth.  The  socket  at  this  time  is  usually  much 
too  large  for  the  root,  and  the  peridental  membrane  is 
correspondingly  thick.  This  is  necessarily  the  case  in  the 
first  instance,  for  the  accommodation  of  the  fully  formed 
crown  of  the  tooth.  After  the  tooth  has  taken  its  position 
the  alveolus  grows  smaller  by  the  deposit  of  bone  on  its 


OSTEOBLASTS  AND  ALVEOLAR  WALLS.       99 

inner  wall,  until  it  is  brought  more  nearly  to  the  size 
required  by  the  root  which  it  is  to  support.  This  occurs 
very  rapidly  as  the  tooth  is  taking  its  position  in  the  arch. 
There  is.  however,  a  movement  of  the  permanent  tooth, 
after  it  has  taken  its  position  in  the  arch,  to  which  I  wish 
to  call  special  attention.  This  takes  place  largely  during 
the  very  noticeable  change  which  occurs  in  the  features 
about  the  age  of  puberty,  but  is  in  progress  from  the  time 
the  permanent  incisors  have  taken  their  places  until  ma- 
turity. I  have  illustrated  this  movement  diagramatically 
in  figs.  52  and  53.  In  each  figure  an  incisor  tooth  is  rep- 
resented in  dotted  lines  with  the  rim  of  the  alveolus  at 
a,  a.  e,  Represents  the  apex  of  the  root,  and  the  dotted 
line  o  the  inner  wall  of  its  alveolus ;  while  the  space  be- 
tween the  lines  c  and  d  shows  its  thick  peridental  mem- 
brane. This  represents  the  position  of  the  tooth  and  its 
alveolus  at  the  age  of  ten  or  twelve  years.  The  tooth 
and  alveolus  drawn  over  this  with  solid  lines  represents 
the  same  tooth  in  the  position  it  will  have  assumed  at  the 
age  of  twenty-one  or  two  years.  The  growth  of  the  alveo- 
lar process  has  carried  the  tooth  in  the  direction  of  its 
length  about  the  distance  represented  by  the  length  of  its 
crown,  or  that  part  of  the  tooth  covered  by  enamel,  as 
represented  in  fig.  53,  which  is  the  maximum  movement 
that  I  have  observed,  while  the  minimum  movement  is 
about  one-half  the  length  of  the  crown,  as  represented  in 
fig.  52.  This  movement  seems  to  be  rather  greater  in 
men  than  in  women,  but  it  presents  considerable  varia- 
tion. I  should  say  that  the  various  points  of  growth  of 
the  bones  of  the  face  are  possibly  not  determined  yet  with 
sufficient  accuracy  for  fixed  points  to  be  established  that 
will  be  without  objection.  The  measurements  I  have 
used  have  been  from  the  anterior  spinous  process  of.  the 
superior  maxillary  bones  (figs.  52  and  53,  J),  to  the  cut- 
ting edges  of  the  superior  central  incisors.  This  measure- 
ment, made  at  ten  or  twelve  years  of  age  and  at  maturity, 


100  OSTEOBLASTS   AND    ALVEOLAR    WALLS. 

indicates  the  movement  shown  in  the  diagrams.  This  is 
a  large  factor  in  the  elongation  of  the  face.  The  move- 
ment in  the  lower  jaw  seems  to  be  about  the  same  as  that 
in  the  upper,  though  it  can  not  be  so  definitely  determ- 
ined. The  principal  growth  concerned  carrying  the  teeth 
forward  for  the  elongation  of  the  arch,  is^  as  is  well 
known,  at  the  back  part  of  the  maxillae,  carrying  the  an- 
terior portions  forward  to  make  room  for  the  molars. 

The  growth  of  the  alveolar  process,  which  carries  the 
tooth  with  it,  as  shown  in  52  and  53,  is  almost  entirely 
from  the  osteal  side  of  the  peridental  membrane,  or  upon 
the  inner  side  of  the  alveolar  wall.  The  elongation  is 
made,  it  is  true,  upon  the  rim  of  the  alveolus,  the  portion 
represented  in  fig,  51  growing  in  a  line  almost  parallel  to 
the  length  of  the  tooth  from  the  points  a,  a,  in  figs.  52 
and  53,  to  the  points  6,  6,  and  in  the  meantime  all  of  the 
space  between  the  wall  (inner)  of  the  former  alveolus  c, 
and  that  of  the  final  alveolus  /,  is  filled  in  by  growth  of 
bone  from  the  osteal  side  of  the  peridental  membrane. 
This  is  all  built  in  originally  with  the  character  of  bone 
represented  at/,  fig.  51.  and  in  figs.  45  and  46,  and  is  re- 
moved by  absorption  and  replaced  by  Haversian  bone,  as 
represented  at  a,  fig.  51.  The  plan  of  this  removal  and 
rebuilding  is  more  particularly  described  in  fig.  24,  and 
on  page  000,  to  which  the  reader  is  referred.  In  this  way 
there  is  a  continuous  activity  in  growth  and  reconstruc- 
tion of  the  alveolar  processes  during  this  time,  in  which 
the  tooth  itself,  except  its  cementum,  is  passive,  the 
dentine  and  enamel  having  previously  completed  their 
growth.  The  movement  represented  in  these  figures  is 
seen  to  be  almost  wholly  in  the  direction  of  the  long  di- 
ameter of  the  tooth,  but  there  is  some  movement  of  the 
crown  of  the  tooth  forward  in  the  direction  of  its  short 
diameter.  This  is  accompanied  by  a  tilting  of  the  crown 
forward,  as  shown.  I  have  often  found  absorption  in  pro- 
gress about  the  point  A,  and  observation  seems  to  indicate 


OSTEOBLASTS   AND   ALVEOLAR   WALLS.  101 

that  a  reduction  occurs  as  represented  from  the  line  h  to 
g.  However,  f i  om  the  want  of  a  fixed  point  from  which 
to  measure,  it  seems  almost  impossible  to  determine  the 
amount  of  the  movement  in  this  direction.  The  tilting  of 
the  crown  forward  is  readily  determined,  however,  by 
taking  the  relative  positions  of  the  tooth  to  a  perpendic- 
ular line. 

I  do  not  know  that  any  previous  writer  has  discussed 
this  subject,  and  I  have  not  now  sufficient  data  at  hand 
for  the  full  presentation  of  it.  Yet  it  is  of  great  import- 
ance in  connection  with  the  formation  of  the  dental  arch, 
and  serves  to  illustrate  the  necessity  of  retaining  it  com- 
plete during  the  formation  of  the  features.  It  also  has  an 
important  bearing  on  the  subject  of  the  correction  of 
irregularities.  1  will  have  more  to  say  of  it  after  having 
considered  the  cementum. 


CHAPTER  XII. 

THE  CEMENTUM  AND  CEMENTOBLASTS. 

The  cementoblasts  or  cement  builders  are  to  the 
cementura  what  the  osteoblasts  are  to  the  bone.  They 
are  the  cells  concerned  in  the  formation  of  the  matrix, 
and  the  deposit  of  lime  salts,  which  enter  into  the  forma- 
tion of  the  cementum.  These  are  cells  of  rather  large 
size  and  of  peculiar  form,  and  are  found  lying  between 
the  principal  fibers  of  the  peridental  membrane  and  upon 
the  surface  of  the  cementum.  While  functionally  they 
hold  the  same  relation  to  the  cementum  that  the  osteo- 
blasts hold  to  the  bone,  they  have  no  resemblance  to  the 
osteoblasts  in  form. 

The  osteoblasts  are  polygonal  cells  inclining  to  the 
round  form,  and  their  longest  diameter  is  often  directed 
away  from  the  bone  upon  which  they  lie,  as  has  been  said 
upon  another  page.  I  have  never  seen  the  cementoblasts 
presenting  these  forms,  but  on  the  contrary,  they  are 
always  distinctly  flattened  cells  with  one  of  their  flat 
sides  resting  upon  the  cementum.  They  are,  indeed,  in 
the  form  of  somewhat  thickened  scales,  of  very  irregular 
outline.  This  irregularity  of  outline  seems  to  be  due  to 
the  position  they  occupy  among  the  principal  fibers  of 
the  peridental  membrane  as  these  latter  pass  out  from  the 
cementum. 

There  is  usually  a  central  mass,  which  is  seen  to  con- 
tain a  regularly  formed  nucleus,  and  from  this  central 
portion  irregular  projections  extend  among  or  between 
the  fibers  of  the  neighborhood. 

The  cells,  with  their  projections,  are  so  placed  that 
they  occupy  all  the  surfaces  of  the  cementum,  except 

102 


THE    CEMENTUM   AND    CEMENTOBLASTS.  103 

that  occupied  by  the  fibers  that  emerge  from  it.  A  better 
idea  of  their  form  can  be  gained  by  examination  of  the 
illustrations,  figs.  54  and  55. 

In  the  first  of  these  I  have  isolated  several  cells,  and 
it  will  be  seen  that  the  form  of  the  projections  from  the 
cell  body  is  such  as  will  fit  in  between  the  fibers.  In  the 
other  illustration  the  fibers  are  shown  cut  across  and  left 
white,  so  that  their  outline  may  be  better  seen.  These 
illustrations  are  taken  from  sections  cut  horizontal  to  the 
surface  of  the  cementum,  and  are  double  stained  with 
hematoxylin  and  neutral  carmine,  which  gives  a  diffusive 
red  stain  to  the  fibers,  while  the  cells  are  of  a  deep  blue. 

Sections  cut  in  any  other  direction  will  fail  to  give  a 
correct  impression  of  the  form  of  these  cells,  but  the 
sections  cut  perpendicular  to  the  surface  are  valuable  as 
illustrating  fairly  the  thickness  of  the  cells.  In  such 
sections  the  cementoblasts  are  seen  in  parts  only.  In  a 
given  focus  of  the  lens,  isolated  parts  of  the  same  cell 
may  appear  as  small  cells  separated  by  fibers,  and  it  is 
practically  impossible  to  connect  them  and  gain  definite 
information  of  their  form  from  such  sections  alone.  The 
projections  among  the  fibers  of  the  membrane  spoken  of 
above  are  not  in  any  proper  sense  processes  from  these 
cells,  but  are  to  be  regarded  as  portions  of  the  cell  body 
which  takes  this  form  on  account  of  the  presence  of  the 
fibers. 

I  have  made  out  true  processes  proceeding  from  these 
cells  in  but  few  instances,  but  enough  to  show  that  they 
exist  upon  a  considerable  number,  if  not  all,  passing  into 
the  cementum  upon  which  the  cells  lie.  However,  they 
are  evidently  not  so  numerous  nor  so  regular  as  the  pro- 
cesses of  the  osteoblasts,  or  if  so  they  are  much  more 
difficult  of  observation.  I  have  never  seen  processes  ex- 
tending from  these  cells  in  a  direction  from  the  cementum 
out  into  the  tissue  of  the  peridental  membrane.  I  think 
it  probable  that  such  processes  exist,  but  it  is  imprac 


104  THE   CEMENTUM   AND   CEMENTOBLASTS. 

ticable  to  display  them  by  stretching  the  tissue  away 
from  the  cementum,  attached  as  it  is  by  strong  fibers,  in 
any  manner  similar  to  that  represented  in  figs.  17  and  18, 
in  case  of  the  non-attached  periosteum. 

In  the  growth  of  the  cementum  some  of  the  cemento- 
blasts  are  included  in  its  substance,  and  persist  as  cement 
corpuscles  in  the  same  manner  as  the  osteoblasts  are  in- 
cluded in  the  bone  as  bone  corpuscles.  The  number  and 
relative  positions  of  these  are,  however,  extremely  irregu- 
lar in  those  animals  that  have  a  thin  cementum.  About 
the  necks  of  the  human  teeth  and  the  teeth  of  the  car- 
nivora,  there  are  usually  no  cement  corpuscles,  but  at 
points  where  the  growth  of  cementum  is  thicker,  they  ap- 
pear in  considerable  numbers ;  and  toward  the  apex  of 
the  root,  where  the  deposit  of  cementum  is  considerable, 
they  may  appear  in  profusion.  That  regularity  of  occur- 
rence which  is  noted  in  bone  corpuscles,  is  not  seen  in 
the  cement  corpuscles.  On  the  contrary,  they  appear  in 
groups  or  in  patches,  while  perhaps  considerable  areas  are 
destitute  of  them.  In  some  of  the  herbivora,  and  notably 
in  the  pig,  they  appear  with  more  regularity,  figs.  57  and 
58. 

The  cement  corpuscles  have  processes  corresponding 
to  those  of  bone  corpuscles,  but  presenting  great  irregu- 
larities. Some  may  show  none  whatever,  others  a  few 
that  may  be  very  short  or  very  long.  While  others  again 
have  a  great  profusion  that  radiate  in  every  direction, 
branch  and  anastomose  with  each  other  and  with  those  of 
neighboring  cells,  forming  an  intricate  network.  Many 
of  the  corpuscles  show  processes  passing  in  one  direction 
only  and  that  is  usually  toward  the  surface  of  the 
cementum. 

The  cementum  is  deposited  upon  the  dentine  and  covers 
the  root  portion  of  the  tooth.  There  is  never  an  attach- 
ment of  the  soft  tissues  with  the  dentine  upon  its  outer 
portion.  Under  some  conditions  the  soft  tissues  may,  in- 


THE   CEMENTUM   AND    CEMENTOBLASTS.  105 

deed,  lie  in  apposition  with  the  dentine  upon  its  surface, 
but  there  is  no  physiological  union  of  the  two  structures. 
The  physiological  connection  of  the  dentine  is  with  the 
dental  pulp,  and  upon  the  pulpal  side  of  the  structure. 
When  the  soft  tissues  lie  in  contact  with  the  opposite 
side,  whether  during  development  or  afterward,  the 
physiological  process  is  either  the  deposit  of  cementum 
upon  the  dentine,  or  absorption  of  the  dentine. 

The  deposit  of  cementum  is  in  the  form  of  lamellae, 
layers,  or  strata,  and  covers  the  root  over  its  entire  sur- 
face. These  lamellae  are  thin,  normally,  toward  the  neck 
of  the  tooth,  and  thicker,  progressively,  as  the  apex  of 
the  root  is  approached,  the  difference  usually  being  very 
considerable.  In  normal  conditions  the  number  of  lamel- 
103  is  about  the  same  on  all  parts  of  the  root,  which  gives 
a  much  thicker  cementum  at  the  apex  than  at  the  cervical 
portion  of  the  root.  The  first  of  these,  or  at  least  the  first 
part  of  the  first  lamellae,  is  usually  hyaline  or  irregularly 
granular  and  ordinarily  contains  no  cement  corpuscles,  or 
at  least  but  few.  The  next  lamella,  especially  high  on 
the  root  portion,  presents  these  corpuscles  very  generally, 
and  they  continue  irregularly  through  the  successive 
lamellae,  provided  always  that  the  individual  lamellae  be 
of  considerable  thickness.  Very  thin  lamellae,  whatever 
their  position,  are  usually  destitute  of  corpuscles,  while 
the  thicker  ones  contain  them. 

These  lamellae  seem  to  represent  periods  of  activity  in 
the  deposit  of  cementum,  each  lamella  being  the  result  of 
a  single  period  of  activity.  If  we  extract  a  tooth  soon 
after  its  eruption  and  examine  its  cementum,  we  shall 
usually  find  it  very  thin  and  containing  but  one  or  two 
lamellae.  A  tooth  from  a  person  who  has  reached  matur- 
ity will  present  a  larger  number  and  the  cement  will  be 
thicker  than  in  that  of  a  child  of  twelve  or  fourteen 
years,  but  not  nearly  so  thick  as  the  cementum  upon  the 
roots  of  teeth  from  old  people  ;  nor  will  it  contain  so  many 


106      THE  CEMENTUM  AND  CEMENTOBLASTS. 

lamellae  of  cementum.  These  layers  are  subject  to  the 
greatest  irregularity,  both  in  the  thickness  of  the  single 
ones  and  in  their  number.  Neither  do  they  present  much 
regularity  at  a  given  age  in  different  persons.  In  all  these 
respects  there  is  the  utmost  irregularity.  The  individual 
lamellae  of  cementum  are  divided  by  lines  that  may  be 
very  distinct,  or  but  imperfectly  seen.  The  mode  of 
preparation  makes  much  difference  in  the  distinctness  of 
these  lines.  Sections  cut  from  decalcified  teeth  and 
mounted  plain  (without  staining),  in  glycerine,  show 
them  very  fairly,  but  they  are  rendered  more  distinct  by 
tinting  slightly  with  a  diffusive  carmine  stain.  These 
lines  I  will  call,  as  Salter  has  done  with  good  reason,  the 
incremental  lines  of  the  cementum.  This  is  appropriate 
from  the  fact  that  each  one  marks  the  divisions  between 
the  lamellae  that  are  laid  upon  the  root,  the  one  upon 
the  other.  Each  successive  lamellae  is  younger  than  the 
preceding  one,  as  we  pass  from  the  surface  of  the  den- 
tine outward. 

In  subperiosteal  growth  of  bone,  incremental  lines  oc- 
cur similar  to  those  in  cementum,  but  they  are  rarely  per- 
manent, for,  as  has  been  said,  subperiosteal  bone  is 
changed  by  the  burrowing  out  of  the  bone  first  formed, 
and  the  deposit  of  Haversian  systems  in  its  stead.  Nothing 
of  this  kind  occurs  in  the  cementum.  It  has  no  Haver- 
sian systems.  In  all  of  my  examinations  of  this  structure, 
I  have  not  in  any  instance  seen  anything  that  could  be 
called  a  Haversian  system  as  these  are  known  in  bone.  I 
have  seen  many  canals  that  seem  to  represent  small  blood- 
vessels included  in  its  structure,  especially  near  the  apex 
of  the  roots  or  between  roots  that  have  become  fused  by 
deposits  of  cementum,  but  these  have  never  had  about 
them  deposits  resembling  the  Haversian  systems  of  bone. 
In  normal  conditions  the  lamellae  of  cementum,  when 
once  deposited,  are  permanent.  They  may  indeed  be  re- 
moved, or  burrowed  into,  as  I  shall  describe  later,  by  ab- 


THE  CEMENTUM  AND  CEMENTOBLASTS.      107 

sorptions  beginning  at  the  surface  and  cutting  through 
the  successive  layers,  but  they  bear  no  resemblance  to  the 
burrowing  for  the  formation  of  Haversian  canals  in  bone. 
Such  absorptions  are  always  refilled  by  a  true  surface  de- 
posit of  cementum,  if  filled  at  all.  See  fig.  61,  a,  a,  a. 

A  correct  understanding  of  these  facts  is  important  to 
the  study  of  hypertrophies  and  absorptions  of  the  cemen- 
tum, which  I  shall  introduce  later.  Furthermore,  the 
cementum  must,  I  think,  be  regarded  as  continuously 
growing,  in  the  sense  of  not  ceasing  at  maturity.  It  is 
very  evident  that  its  growth  does  not  cease  with  the 
maturity  of  the  tooth,  nor  with  the  maturity  of  the  person. 
We  find  pretty  uniformly  a  thin  cementum  upon  the 
teeth  of  the  young,  and  a  thick  cementum  upon  the  teeth 
of  the  old ;  and  when  a  great  number  are  examined  from 
persons  of  known  ages,  it  will  be  found  that  there  is  a 
continuous  increase  in  thickness  and  in  the  number  of  in- 
cremental lines.  But  in  such  examination  great  varia- 
tions from  any  given  rule  will  be  noted.  One  set  of  sec- 
tions cut  from  the  lower  molar  of  a  man,  about  seventy 
years  old,  shows  on  the  sides  of  the  roots  forty- two  lamel- 
lae easily  distinguishable  and  counted  with  a  half  inch 
lens.  While  over  the  apex  of  the  root,  which  presents 
some  hypertrophy,  there  are  a  few  additional  lamellae. 

The  incremental  lines  are  not  always  regular  in  their 
distribution  over  the  tooth's  root.  Sometimes  a  lamella 
is  laid  down  that  covers  only  a  part  of  the  root  and  two 
lines  merge  into  one.  This  seems  to  show  that  there  has 
been  a  local  activity  of  deposit  over  part  of  the  surface, 
that  has  not  extended  to  the  entire  root.  Some  of  the 
incremental  lines  seen  toward  the  apex  of  the  root  where 
the  cementum  is  thicker  may  disappear  as  the  neck  of  the 
tooth,  where  the  cementum  is  thinner,  is  approached. 
Again,  regions  will  be  found  in  which  it  is  evident  that 
certain  lamellae  of  the  cementum  have  been  removed  by 
absorption. 


108  THE   CEMENTUM   AND   CEMENTOBLASTS. 

FIBERS   OF   THE   CEMENTUM. 

As  I  have  said  the  fibers  of  the  peridental  membrane 
spring  out  of  the  cementum.  These  fibers  pass  through 
all  of  its  lamellae  to  the  first  one  laid  on  the  dentine  and 
part  way  through  that,  no  matter  what  the  thickness  may 
be.  In  most  localities  in  the  human  cementum  these 
fibers  are  not  continuous,  but  are  broken  at  some  of  the 
incremental  lines.  At  some  such  points  they  have  cer- 
tainly been  detached  by  absorption,  but  in  most  instances 
this  cause  of  detachment  can  not  be  made  out  satisfactor- 
ily. On  account  of  this  frequent  breaking  it  is  not  gen- 
erally possible  to  follow  individual  fibers  from  the  peri- 
dental  membrane  entirely  through  the  cementum,  even 
in  sections  cut  parallel  with  them,  though  they  may  be 
seen  in  all  its  lamellse.  In  the  pig  the  fibers  are  much 
larger  and  less  thickly  placed  than  in  man.  This  renders 
the  tracing  of  individual  fibers  from  the  membrane  into 
this  substance  comparatively  easy  (Fig.  57).  In  the  pig, 
also,  there  is  a  great  thickness  of  cementum,  compara- 
tively, formed  in  a  few  months,  and  this  presents  but  a 
few  incremental  lines  at  which  the  fibers  are  broken.  We 
can,  therefore,  follow  individual  fibers  through  its  entire 
thickness  in  sections  cut  parallel  with  them.  In  man,  the 
fibers  are  so  much  broken  at  the  incremental  lines  that  it 
is  only  now  and  then  that  we  are  able  to  find  individual 
fibers  traversing  its  whole  thickness. 

Much  of  the  cementum  of  man,  especially  that  about 
the  necks  of  the  teeth,  when  so  stained  as  to  show  them 
clearly,  seems  almost  as  if  made  up  of  fibers.  These  are 
usually  small,  placed  close  together,  and  run  pretty 
squarely  outward,  pursuing  a  straight  course,  (Fig.  59, 
5,  c,)  but  farther  up  on  the  root,  where  the  cementum  is 
thicker,  they  are  often  found  curved  in  various  directions, 
and  many  times  we  shall  notice  an  abrupt  change  of 
direction  at  an  incremental  line.  Some  spaces  or  patches 
will  be  noticed  in  which  the  fibers  seem  to  be  absent. 


THE  CEMENTUM  AND  CEMENTOBLASTS.      109 

These  fibers  have  been  noticed  by  various  writers,  and 
not  a  few  have  spoken  of  them  as  the  fibers  of  Sharpey, 
while  others,  Salter  and  Abbott,  seein  to  have  mistaken 
them  for  canaliculi  similar  to  those  of  dentine.  This  error 
can  scarcely  be  avoided  if  the  examination  has  been  con- 
fined to  the  dried  specimen,  for  it  seems  that  many  of  the 
fibers  are  but  imperfectly  calcified,  and  in  drying  suffer 
shrinkage  to  such  an  extent  as  to  give  that  appearance. 
I  have  a  number  of  sections  in  my  collection  that  show 
this. 

These  are  the  principal  fibers  of  the  peridental  mem- 
brane included  in  the  cementum  in  its  growth,  and  fur- 
nish the  means  of  making  firm  hold  of  the  peridental 
membrane  upon  the  root  of  the  tooth.  They  are  white 
connective  tissue  fibers,  the  ends  of  which  are  included  in 
the  matrix  of  the  cementum  sufficiently  to  make  them 
apparent  when  the  lime -salts  are  removed,  but  when  both 
are  calcified,  they  can  not  be  demonstrated  except  in  cases 
in  which  there  is  imperfect  calcification  of  the  fibers,  as 
has  been  mentioned  above. 

A  very  beautiful  demonstration  of  these  fibers  may  be 
had  in  the  cross-section  of  them,  i.  e.,  in  moist  sections  of 
the  cementum  cut  horizontal  to  its  surface.  If  these  be 
very  thin,  stained,  and  mounted  in  balsam,  they  will 
show  the  fibers  cut  across  especially  well.  In  this  case 
there  will  generally  be  such  a  shrinkage  that  a  part  of 
the  circumference  of  the  fiber  will  be  parted  from  its 
matrix,  showing  it  plainly ;  and  by  close  focusing  the 
whole  outline  of  the  fiber  may  be  clearly  seen.  In  some 
very  thin  parts  of  sections  the  fibers  may  drop  out  of  their 
alveoli,  leaving  openings.  This  was  the  case  in  the  sec- 
tion from  which  fig.  56  was  made.  In  many  very  thin 
sections  parallel  with  the  fibers,  we  may  see  about  broken 
edges  the  fibers  protruding  from  the  margin,  as  is  shown 
in  fig.  57,  d,  d.  This  is  much  as  I  have  illustrated  the 
residual  fibers  of  bone  as  doing  in  fig.  21. 


110      THE  CEMENTUM  AND  CEMENTOBLASTS. 

The  clearness  and  regularity  of  the  appearance  of 
these  fibers  of  the  cementum  in  my  preparations  make  it 
a  matter  of  great  surprise  to  me  that  they  have  not  been 
before  described  by  writers  on  dental  histology.  I  can 
only  account  for  its  oversight  by  the  fact  that  very  few- 
studies  of  the  peridental  membrane  have  been  made,  and 
these  seem  to  have  been  only  casual,  and  thus,  the  con- 
nection of  the  fibers  of  the  two  structures  have  escaped 
notice.  In  this  way  the  appearance  of  fibers  in  the 
cementum  has  been  passed  as  something  not  understood, 
or  they  have  been  wrongly  interpreted.  However,  most 
of  the  studies  of  this  structure  have  been  made  from 
dried  sections  in  which  the  fibers  could  not  be  dem- 
onstrated. 


CHAPTER  XIII. 

IRREGULARITIES    IN    THE   GROWTH   OF   CEMENTUM, 

Hypertrophies  of  the  cementum  have  been  under  dis- 
cussion for  many  years  and  generally  they  have  been  re- 
garded as  pathological  phenomena.  I  think,  however, 
that  the  careful  student  must  admit  that,  in  the  vast 
numbers  that  occur,  there  are  comparatively  few  in- 
stances in  which  the  pathological  character  of  these  is 
fairly  made  out.  They  have  been  regarded  as  connected 
with  all  manner  of  aches  and  pains.  I  wish  now  to  call 
attention  to  a  mode  of  study  of  these,  which,  if  followed, 
will,  I  think,  dispel  most  of  these  notions.  Not  that  I 
wish  to  affirm  that  in  no  case  a  hypertrophy  of  the 
cementum  may  be  related  to  a  process  of  disease,  but 
rather  to  show  that  this  is  not  necessarily  the  case  and  as 
a  matter  of  fact  is  very  rarely  so.  They  are  to  be  regarded 
rather  as  irregularities  than  as  pathological  phenomena. 

I  have  already  said  that  the  cementum  is  to  be  regard- 
ed as  continuously  growing  in  the  sense  that  its  growth 
continues  to  old  age.  It  may  be  found  augmenting  in 
thickness  in  persons  seventy  years  old  and  the  process  be 
perfectly  normal.  I  wish  also  to  further  emphasize  the 
fact  that  the  manner  of  the  growth  is  by  interrupted  ac- 
cretion, or  in  periods  of  activity  and  rest.  The  inter- 
vals of  inactivity  are  probably  very  great  sometimes, 
but  the  examination  of  the  cementum  of  any  con- 
siderable number  of  persons  at  thirty  years  of  age,  and 
comparisons  with  a  similar  number  at  fifty  years,  will 
show  that  there  has  been  a  pretty  regular  increase  in  the 
thickness  and  in  the  number  of  lamellae  of  the  cementum. 
If  those  of  fifty  are  again  compared  with  those  of  seventy, 

111 


112       IRREGULARITIES   IN   GROWTH   OF   CEMENTUM. 

a  farther  increase  in  thickness  and  number  of  lamellae 
will  be  manifest.  This  growth  takes  place  at  irregular 
intervals  of  time,  which  is  expressed  in  this  lamellation. 
The  lamellae  are  laid  the  one  upon  the  other  successively 
and  the  outer  ones  are  of  course  the  last  in  the  order  of 
growth. 

When  a  tooth  presents  through  the  gum  and  has  taken 
its  place  in  the  arch,  its  cementun  will  generally  present 
but  one  layer ;  but  if  it  has  been  brought  into  use  for 
a  time  it  is  likely  to  present  two  or  three,  one  formed 
contemporaneously  with  the  root  and  one  probably  when 
it  was  first  brought  into  contact  with  its  antagonist  or 
possibly  while  it  was  being  protruded  after  the  growth  of 
the  root  was  accomplished.  It  seems  probable  also  from 
examinations  I  have  made,  that  there  often  several  la}rers 
of  cementum  deposited  during  the  movements  of  the 
teeth  connected  with  the  lengthening  of  the  face  which 
was  illustrated  in  Figs.  52  and  53.  At  any  rate  differ- 
ences in  this  regard  are  observed,  whatever  be  their  cause. 
As  the  tooth  grows  older  new  lamellae  are  laid  down.  It 
must  be  admitted  that  the  study  of  these  lamellae  has  not 
as  yet  been  sufficient  for  us  to  form  any  definite  idea  as 
to  their  relation  to  the  age  of  the  individual  after  the  first 
two  or  three  have  been  laid  down.  But  however  this 
may  be,  it  will  be  found  upon  examination  that  every  case 
of  irregularity  in  growth  will  be  connected  with  one  or 
more  of  the  lamellae,  and  the  relative  time  of  the  irregu- 
larity of  growth  to  the  deposit  of  the  individual  lamellae 
can  be  made  out. 

On  applying  this  mode  of  study  to  the  irregularities 
of  growth  in  my  collection,  I  find  a  great  variety.  They 
are  connected  with  the  lamellae  in  all  sorts  of  ways.  Some 
belong  to  a  single  lamellae,  others  include  several,  while 
others  again  include  all  of  the  series  from  the"  first  to  the 
last,  each  one  being  thicker  in  the  hypertrophied  portion 
than  elsewhere.  Now  it  is  perfectly  evident  that  such  a 


IRREGULARITIES   IN    GROWTH    OF   OEMENTUM.        113 

hypertrophy,  as  this  latter,  lias  been  forming  with  each 
successive  growth  of  the  cementum  from  the  first  to  the 
last,  while  those  that  are  confined  to  one  or  a  few  lamellae 
have  begun  and  ceased  with  the  deposit  of  these.  There 
is  no  such  thing  as  interstitial  growth  of  the  cementum, 
and  no  thickening  of  the  lamellae  can  occur  after  another 
is  deposited  over  it. 

Among  these  hypertrophies  confined  to  one  or  a  few 
lamellae,  the  greatest  variety  will  be  found.     I  have  speci- 
mens from  teeth  just  erupted  showing  hypertrophy  of  the 
first  and  only  lamellae  yet  deposited.     But  these  are  more 
rare  than  those  connected  with  the  second  or  third.     It 
seems  to  be  with  the  latter  that  the  greater  number  of  the 
irregularities   are  connected  ;    though  a  goodly   number 
will  be  found  beginning  with  those  deposited  later ;  and 
some  are  connected  with  the   last  one,  even  in  very  old 
persons.     These  last  have  of  course  occurred  late  in  life 
while  the  others  have  occurred  at  an  earlier  age.     The 
greater  number  of  the  irregularities  in  the  deposit  of  the 
cementum  are  probably  connected   with   some    especial 
strain  upon  the  tooth,  and  their  causation  probably  cor- 
responds with  that  of  the  absorptions  which  are  yet  to  be 
studied.     We  generally  find  these  combined  in  the  same 
tooth  and  occurring  at  about  the  same  time.     That  is  to 
say,  the  absorptions  of  the  cementum  are  shown  in  the 
lamellae  that  lie  next  beneath  those  that  show  the   con- 
dition   of  hypertrophy  but  are  generally  upon   another 
portion  of  the  root,  which  may  be  contiguous  or  upon  the 
other  side.     I  frequently  see  these   latter  that  have  cut 
away  the   first  two  lamellae,  penetrated  the  dentine  to 
some  depth  and  have  been  refilled  with  cementum  in  con- 
nection with  the  deposit  of  the  third  or  fourth  lamella. 
Now  these  facts  have  prompted  this  thought ;  the  tooth 
makes  its  growth  and  presents  its  crown  to  its  antagonist. 
At  first  the  cusps  of  the  one  do  not  strike   fairly  into  the 
sulci  of  the  other.     This  causes  a  lateral  strain  upon  the 


114       IRREGULARITIES    IN   GROWTH   OF    CEMENTUM. 

peridental  membrane  as  the  tooth  is  forced  to  one  side 
sufficiently  for  the  proper  adjustment  of  the  cusps.  A 
portion  of  the  membrane  is  put  upon  the  stretch  and 
probably  the  cementoblasts  are  stimulated  to  increased 
deposit  of  cementum  during  this  interval.  This  results 
in  an  irregularity  of  growth  which  may  be  in  connection 
with  a  single  general  lamella  of  cementum,  or  it  may  be 
only  a  partial  lamella  confined  to  one  part  of  the  root. 
At  the  same  time  absorption  may  have  occurred  in  an- 
other part  as  upon  the  opposite  side,  removing  some  por- 
tion of  the  layers  previously  formed,  or  forming  irregular 
openings  throughout  the  whole  thickness  of  the  previous 
formation  and  penetrating  the  substance  of  the  dentine. 
These  latter  are  now  refilled  with  cementum  with  the  next 
lamella  deposited,  and  afterward  the  deposit  may  take 
place  regularly  over  both  the  hypertrophy  and  the  absorp- 
tion area,  and  these  will  be  found  covered  with  a  number 
of  regularly  formed  lamellae. 

Such  a  theory  seems  very  weak,  however,  when  con- 
fronted with  thickenings  like  the  one  shown  in  fig.  60, 
which  is  confined  to  the  first  layer,  while  the  subsequent 
ones  are  very  regularly  formed.  This  was  a  thickened 
portion  on  the  side  of  a  root  of  a  cuspid  tooth.  It  can  not 
be  stated  positively  that  this  was  all  formed  before  there 
was  a  contact  with  its  antagonist,  but  its  deposit  was 
certainly  continuous  with  the  layer  formed  contempora- 
neously with  the  development  of  the  tooth.  I  have 
found  such  thickenings  of  the  first  layer  in  teeth  not  yet 
fully  developed  upon  which  there  was  as  yet  but  the  one 
layer  of  cementum  deposited.  This  seems  to  show  that 
these  irregularities  do  not  depend  wholly  upon  extraneous 
influences. 

Other  instances  will  be  found  in  which  on  some  part 
of  the  root  there  will  be  a  thickened  -portion  confined  to  a 
single  layer  belonging  to  a  much  later  date,  as  the  one 
illustrated  in  fi^.  59.  This  was  on  the  distal  side  of  the 


IRREGULARITIES   IN   GROWTH   OF    CEMENTUAL       115 

root  of  a  molar  near  the  gingival  border,  and  so  far  as 
could  be  made  out  without  a  history  of  the  case,  the  con- 
ditions point  to  an  irregular  strain  upon  the  tooth  as  a 
cause.  The  crown  of  the  adjacent  bicuspid  had  been 
broken  away  a  number  of  years  previously,  apparently, 
and  this  tooth  had  leaned  forward  over  the  remaining 
root.  Upon  the  mesial  side  of  the  anterior  root  there 
were  several  absorptions  affecting  the  lamellae  next  be- 
neath the  one  hypertrophied  upon  the  distal  side.  Ap- 
pearances indicate  that  this  occurred  at  an  age  of  up- 
wards of  fifty  years. 

Other  cases  occur  in  which  there  is  an  increased  thick- 
ness in  each  successive  layer  over  the  same  spot.  These 
are  found  mostly  about  the  apex  of  the  root  upon  one 
side,  or  covering  the  entire  apex  in  the  form  of  a  rounded 
knob.  They  may  become  thinner  gradually  toward  the 
neck  of  the  tooth  or  cease  abruptly.  In  the  latter  case 
absorption  areas  will  generally  be  found  around  the 
border  of  the  hypertrophied  portion.  I  have  illustrated 
such  a  case  in  fig.  61,  from  a  hypertrophy  of  the  root  of  a 
superior  bicuspid.  It  will  be  noted  that  in  this  case  the 
roots  were  originally  separate,  and  that  they  became  fused 
together  with  the  deposit  of  the  second  lamella  of  the 
cementum ;  and  that  this  lamella  presents  the  greatest 
thickness,  while  those  deposited  later  are  progressively 
thinner;  therefore  a  large  part  of  this  deposit  must  have 
occurred  early  in  life.  Connected  with  this,  areas  of  ab- 
sorption have  occurred  at  d,  d,  d,  which  have  narrowed 
the  root  at  that  part,  increasing  the  nobbed  appearance 
of  the  apex.  It  will  be  seen  that  these  absorption  areas 
have  been  refilled  with  cementum  in  connection  with  the 
deposit  of  certain  lamellae. 

I  have  seen  a  number  of  cases  of  hypertrophy  similar 
to  the  one  last  described,  that  I  supposed  resulted  from 
the  loss  of  an  antagonist  and  a  consequent  partial  protru- 
sion of  the  tooth  from  its  socket.  But  most  of  these 


116        IRREGULARITIES   IN   GROWTH   OF   CEMENTUM. 

showed,  when  sections  were  made,  that  the  thickening 
had  begun  very  early  in  the  .history  of  the  tooth.  The 
second  and  third  lamellae  being  the  thicker,  necessarily 
excluded  the  loss  of  the  antagonist  as  the  cause.  Other 
cases  occur,  in  which  the  increased  growth  belongs  to  the 
lamellae  last  deposited,  and  in  these  the  loss  of  the  antag- 
onist would  seem  to  be  a  probable  cause.  Our  knowledge 
of  the  subject  is  not  yet  sufficient  for  the  satisfactory 
determination  of  the  cause  of  these  irregularities  in  any 
case,  but  the  suppositions  given  may  lead  to  further  study 
and  thought,  and  lead  to  something  more  satisfactory. 
In  the  meantime  it  seems  evident  that  the  anomaly  should 
not  be  considered  as  a  pathological  state,  but  rather  as  an 
irregularity  of  development.  Yet  these  enlargements, 
when  considerable,  may  impinge  upon  the  surrounding 
tissue  in  such  manner  as  to  induce  conditions  of  a  patho- 
logical nature. 

Another  point  of  interest  should  be  noted  in  this  con- 
nection. It  is  a  well-known  fact  that  cementum  and 
bone  never  unite.  At  least  no  well  authenticated  case  is 
on  record.  In  reptiles  and  fishes  the  osseous  union  of  the 
teeth  with  the  bones  is  the  normal  condition.  With  this 
fact  before  us,  and  considering  the  great  similarity  of 
cementum  and  bone,  it  seems  quite  remarkable  that  such 
a  union  should  not  sometimes  occur.  In  the  study  of  this 
subject  I  often  find  an  exceedingly  thin  peridental  mem- 
brane dividing  the  hypertrophied  cementum  from  its  alve- 
olus. But  there  is  always  some  soft  tissue.  I  do  not 
remember  of  any  case  occurring  high  up  on  the  root 
about  which  the  membrane  was  unusually  thick.  The 
rule  is  that  it  is  thinner,  than  about  the  parts  not  hyper- 
trophied. The  bone  forming  the  alveolus  is  also  apt  to  be 
more  than  usually  cancellated. 

When  cementum  in  its  growth  approaches  cementum 
the  case  is  entirely  different.  On  coming  together  fusion 
occurs  whether  the  roots  belong  to  one  tooth  or  to  differ- 


IRREGULARITIES    IN   GROWTH    OF    CEMENTUM.        117 

ent  teeth.  In  this  way  the  roots  of  neighboring  teeth  be- 
come fused  together  in  a  considerable  number  of  instances. 
Sometimes  this  seems  to  have  occurred  contemporaneously 
with  the  development  of  the  teeth,  and  the  subsequent 
thickening  of  the  cementum  obliterates  the  point  of  junc- 
tion to  such  an  extent  as  to  give  the  appearance  of  a 
single  root  with  two  crowns.  But  many  of  the  cases  seen 
have  evidently  occurred  comparatively  late  in  life.  I 
have  seen  a  number  of  specimens  in  which  it  seemed  that 
the  fusion  of  the  roots  had  occurred  on  account  of  the 
teeth  having  been  forced  out  of  position,  especially  in 
molars,  which  had  inclined  forward  after  the  loss  of  the 
next  tooth  anterior  to  them,  and  the  roots  pressed  back- 
ward in  such  a  way  as  to  come  in  contact  with  the  roots 
of  a  posterior  tooth.  Again  spherules  of  calcific  material 
occur  in  the  peridental  membrane.  As  has  been  noted, 
cementum  may  be  deposited  upon  these,  and  this  will 
fuse  with  the  cementum  of  the  root  of  the  tooth. 

These  facts  taken  together  seem  to  show  that,  while 
cementum  and  bone  are  so  very  similar  in  structure,  there 
is  a  radical  difference  in  the  specialized  cells  by  which 
they  are  formed,  which  prevents  them  from  coalescing  in 
their  functional  activities.  Yet  these  cells  are  developed 
within  the  meshes  of  the  same  membrane,  the  fibers  of 
which  span  the  space  from  the  one  hard  formation  to  the 
other. 


CHAPTER  XIV. 

ABSORPTIONS    OCCURRING    IN   THE   ALVEOLUS. 

The  absorptions  occurring  in  the  alveolus  are  of  much 
interest  and  practical  importance  to  the  practitioner. 
They  are  very  frequent,  occur  under  various  conditions 
and  circumstances,  and  may  be  of  any  extent,  from  the 
slightest  erosion  of  the  surface  of  the  root  of  the  tooth, 
or  of  its  alveolar  wall,  to  the  complete  removal  of  either 
or  both.  It  is  by  absorption  that  the  roots  of  the  tempo- 
rary or  milk  teeth  are  removed  to  give  place  to  the  per- 
manent or  adult  teeth.  And  so  far  as  microscopic  study 
of  the  subject  can  determine,  it  is. by  precisely  the  same 
plan  that  the  roots  of  permanent  teeth  are  occasionally 
absorbed,  either  in  part  or  completely.  So  far  as  has  yet 
been  determined,  it  is  this  same  process  of  absorption  that 
is  the  great  enemy  with  which  we  have  to  contend,  in  the 
various  operations  of  replanting,  transplanting  and  im- 
planting natural  teeth. 

The  subject  of  the  absorption  of  the  roots  of  the  tem- 
porary teeth  does  not  properly  come  within  the  scope  of 
this  work,  except  incidentally  for  comparison  with  other 
absorptions.  A  study  of  the  physiological  errors  that  occur 
in  the  absorption  of  the  roots  of  the  temporary  teeth  will 
do  much  to  explain  some  things  that  seem  very  strange 
in  the  absorptions  which  occur  in  the  alveoli  of  the  adult 
teeth.  By  physiological  errors,  I  mean,  as  has  previously 
been  said,  an  action  of  the  tissues  which  is  purely  physio- 
logical in  form,  but  going  beyond  the  needs  of  the  time 
and  perhaps  calling  for  a  counter-action  on  the  part  of 
the  adjacent  tissues  for  its  correction ;  but  not  going  to 
an  extent  that  can  properly  be  classed  as  pathological. 

118 


ABSORPTIONS   IN   THE   ALVEOLUS.  119 

In  the  consideration  of  the  soft  tissues  such  errors  are 
not  readily  detected,  because  all  traces  of  them  is  soon 
effaced ;  but  in  the  study  of  the  bones,  and  especially  of 
the  teeth,  where  these  errors  remain  written  indelibly  in 
the  structure  in  which  they  have  occurred,  possibly  many 
years  before,  we  may,  after  sufficient  observation,  trace 
their  progress  and  subsequent  correction  with  almost  the 
same  certainty  that  we  can  trace  a  wellworn  pathway 
through  the  wooded  hills. 

The  process  of  absorption  has  been  spoken  of,  its  pe- 
culiar cells  illustrated  and  described,  and  its  effects  upon 
the  hard  tissues  detailed,  in  the  previous  pages.  It  is 
generally  performed,  we  may  say  always,  when  any  con- 
siderable mass  of  hard  tissue  is  to  be  slowly  removed,  by 
the  specialized  cells  known  as  osteoclasts.  How  these 
cells  perform  this  function  is  not  yet  perfectly  clear.  It 
seems  that  they  elaborate  and  evolve  from  themselves  a 
substance  which  dissolves  the  hard  tissues  with  which 
they  may  be  in  contact.  Some  observers,  as  Krause,  re- 
gard this  substance  as  being  lactic  acid,  while  many 
others  seem  unwilling  to  express  an  opinion.  The  action 
upon  the  hard  tissue  is  certainly  different  from  that  of 
lactic  acid,  in  that  there  is  very  little  softening  of  tissue 
upon  which  it  acts  farther  than  the  portion  actually 
liquefied  and  removed.  The  surface,  being  absorbed,  is 
thrown  into  elevations  and  depressions  by  the  form  of 
the  cells  acting  upon  it,  but  the  surface  of  each  of  these 
depressions  will  be  found  to  be  clean,  smooth  and  hard, 
and  when  dried  will  glisten  like  a  polished  surface.  The 
osteoclasts  are  not  attached  to  the  surface  of  the  bone  or 
tooth  by  any  mechanical  means  whatever ;  they  simply 
lie  agairist  the  surface  and  are  detached  with  the  least 
movement.  They  act,  however,  only  when  lying  in  con- 
tact with  the  surface.  Any  intervening  substance  what- 
ever will  prevent  their  action.  Therefore,  the  formation 
of  an  abscess  with  pus  lying  about  the  end  of  the  root 


120  ABSORPTIONS   IN   THE   ALVEOLUS. 

of  a  temporary  tooth,  so  long  as  it  lasts,  is  a  bar  to  the 
absorptive  process.  This  may  act  in  two  ways.  1st.  The 
presence  of  the  pus  may  separate  the  cells  from  the 
tooth's  root.  2d.  The  pathological  condition  may  pre- 
vent the  physiological  action  of  the  cells.  The  process 
of  absorption  is  always  to  be  regarded  as  physiological, 
but  the  error  of  direction  and  extent  may  be  so  great  as 
to  constitute  a  pathological  condition,  as  when  the  root 
of  a  permanent  tooth  is  wholly,  or  in  a  great  part,  re- 
moved by  this  process. 

The  tissue  acted  upon  in  absorption  is  always  passive. 
On  this  point  there  seems  to  have  been  a  difference  of 
opinion,  some  writers  supposing  that  the  absorption  of 
bone  was  performed  in  part  by  the  bone  corpuscles. 
There  may  be  some  forms  of  disease  of  the  bones  in 
which  this  is  the  case,  as  claimed  by  Cornil  and  Ranvier ; 
but  certainly  there  is  no  such  thing  in  the  physiological 
absorptions.  The  root  of  a  tooth  that  has  lost  its  pulp, 
and  consequently  the  vitality  of  its  dentine,  will  be 
absorbed  as  readily  and  as  completely  as  the  living  tissue 
provided  always  that  the  tissues  in  contact  with  the  root 
be  in  a  physiological  condition.  I  have  frequently  noted 
the  absorption  of  the  root  of  a  temporary  tooth  after  the 
healing  of  alveolar  abscess  ;  but,  if  the  abscess  continues, 
the  absorption  will  generally  fail  in  part  or  entirely.  For 
the  performance  of  absorption,  then,  it  is  required  that 
the  physiological  action  of  the  cells  be  not  seriously 
impaired.  At  the  same  time,  the  clinical  history  of  cases 
seems  to  show  that  a  moderate  degree  of  irritation  or 
inflammatory  action  may  hasten,  or  even  be  the  condition 
of  the  beginning  of  many  of  the  absorptions.  It  is  not 
yet  clearly  made  out  that  the  absorption  of  bone  in  condi- 
tions of  inflammation  is  always  the  same  process  as  that 
which  occurs  physiologically,  but  I  will  say  that  in  all  the 
absorptions  within  the  alveolus  which  I  have  yet  exam- 
ined, the  process  has  been  identical  with  the  physiological 


ABSORPTIONS   IN   THE   ALVEOLUS.  121 

removal  of  the  roots  of  the  temporary  teeth ;  but  is  mani- 
fested in  directions  and  in  forms  that  are  often  erratic  in 
the  extreme. 

I  have  examined  very  closely  the  condition  of  the  bone 
corpuscles  in  the  immediate  neighborhood  of  areas  of 
absorption  in  various  regions  and  conditions,  and  have 
never  seen  any  evidence  whatever  that  they  took  part  in 
the  process.  I  have,  in  a  number  of  instances,  found  the 
bone  corpuscle  uncovered  by  absorption  and  their  pro- 
cesses removed  up  to  the  body  of  the  cell,  and  yet  no 
change  could  be  discovered  in  the  condition  of  the  cell 
itself.  There  is  certainly  no  enlargement  of  the  chamber 
in  which  it  lies.  It  seems  to  be  entirely  passive.  Pre- 
cisely the  same  is  true  of  the  cement  corpuscles.  The 
dentine  is  also  removed,  and  the  dental  fibres  cut  away 
without  the  least  change  occurring,  either  in  the  remain- 
ing parts  of  the  fibrils,  or  the  dentine  of  the  neighborhood. 

All  of  this  illustrates  the  fact  that  these  tissues  when 
once  formed  become  passive  agents.  Not  that  all  of  their 
parts  have  become  inert  material  devoid  of  life,  but  they 
are  for  the  most  part  composed  of  formed  material,  in 
which  physiological  activity  is  reduced  to  a  minimum. 

Many  of  the  irregular  phases  of  the  absorptive  process 
might  be  illustrated  by  the  examination  of  the  roots  of 
the  temporary  teeth.  Perhaps  very  few  of  these  are 
regularly  removed  proceeding  from  the  apex  of  the  root 
to  the  crown.  Indeed,  the  more  common  form  is  for  the 
absorption  to  begin  some  distance  down  on  the  side  of 
the  root,  cutting  a  deep  cleft.  Then  it  will  begin  at 
some  other  point  and  do  the  same  thing,  and  at  another, 
and  so  on.  These  will  finally  merge  into  the  great  gap  in 
the  substance  of  the  root,  and  the  process  will  perhaps 
proceed  more  rapidly  in  the  destruction  of  the  remaining 
portion.  We  have  no  evidence  that  during  this  time  the  ab- 
sorptive process  produces  any  inconvenience  to  the  young 
animal,  or  the  child.  It  is  not  until  the  tooth  is  materially 
16 


122  ABSORPTIONS   IN   THE   ALVEOLUS. 

loosened  by  the  loss  of  its  root  that  inconvenience  is  felt. 
But  during  the  earlier  part  of  this  process  it  seems  to 
proceed  with  much  uncertainty  and  indecision  (if  such 
terms  are  admissible),  for  we  find  many  instances  in 
which  the  absorption  bar-  proceeded  for  a  time  and  then 
ceased — not  only  ceased,  but  the  work  of  repairing  the 
breach  has  been  undertaken  by  the  building  in  of  new 
cementum. 

I  offer  an  illustration  of  such  a  case,  taken  from  the 
temporary  tooth  of  a  pig,  in  fig.  62.  In  this  case  a  large 
breach  extending  far  into  the  dentine  had  been  made  in 
the  side  of  the  root,  nearly  midway  its  length,  by  absorp- 
tion, and  at  f  the  bone  had  grown  forward  toward  the 
absorbed  area.  Now  a  change  occurred.  Cementum  is 
again  deposited  for  the  repair  of  the  breach,  and  this  is 
laid  down  over  the  cut  ends  of  the  dentinal  canals,  upon 
the  dentine,  covering  it  over  smoothly  and  evenly  in  this 
case,  though  it  is  not  always  done  so  regularly.  It  will 
be  noted  that  the  gap  in  the  dentine  is  not  repaired  by  a 
new  formation  of  dentine.  Such  gaps  are  always  repaired 
by  cementum,  if  repaired  at  all.  In  many  cases  there  is 
a  much  greater  deposit  of  cementum  of  repair  than  in 
this,  but  this  one  is  sufficient  to  show  that  cementum  may 
be  laid  down  upon  the  dentine  denuded  of  its  cementum, 
which  is  a  point  of  no  mean  importance  in  these  days  of 
the  study  of  the  various  forms  of  replantation,  and  of  the 
amputation  of  roots  of  teeth.  Fig.  65  illustrates  the  same 
thing  as  occurring  upon  the  root  of  a  permanent  molar. 

Passing  now  to  the  permanent  teeth,  I  will  first  notice 
the  absorptions  occurring  in  the  alveolar  wall.  These  are 
very  numerous,  and  may  be  studied  by  preparing  sections 
of  any  of  the  teeth  of  the  adult ;  but  the  best  studies  will 
be  had  from  the  alveoli  of  teeth  that  are  at  the  time  un- 
dergoing change  of  position  from  any  cause,  such  as  the 
loss  of  a  neighboring  tooth,  continued  pressure,  or  the  in- 
cisors (and  I  suppose  the  molars  also)  during  that  change 


ABSORPTIONS  IN  THE  ALVEOLUS.         123 

of  position  which  occurs  during  the  lengthening  of  the 
face,  which  was  illustrated  and  described  in  chapter  XI. 
Under  any  of  these  circumstances  changes  in  the  alveolus 
and  the  attachment  in  the  principal  fibers  of  the  peri- 
dental  membrane  occur,  and  these  seem  to  call  for  ab- 
sorption and  rebuilding  of  bone.  In  fig.  63  I  present  an 
illustration  of  this,  taken  from  the  middle  portion  of  the 
anterior  wall  of  an  incisor.  The  upper  portion  of  the  il- 
lustration is  toward  the  crown  of  the  tooth.  This  illus- 
tration shows  especially  well  the  method  by  which  the 
fibers  of  the  peridental  membrane  become  detached  and 
reattached  during  movements  of  the  tooth  in  its  alveolus. 
No  very  considerable  absorption  areas  are  seen,  but  groups 
of  osteoclasts  appear  at  very  frequent  intervals,  as  shown 
at  d,  d,  d,  which  lie  in  the  lacunse  of  Howship,  absorbed 
into  the  surface  of  the  bone.  At  all  such  points  the  fibers 
are  detached.  Indeed,  these  fibers  seem  to  disappear  with 
the  appearance  of  the  osteoclasts,  but  wherever  the  bone 
is  not  covered  by  these  cells  the  fibers  are  found  to  be  in 
position.  At/ it  will  be  noted  that  a  portion  of  new  bone 
has  been  built  on  to  the  old,  in  which  the  ends  of  the 
fibers  are  secured.  In  this  way,  it  seems,  absorptions 
and  changes  in  the  alveolus  may  occur  slowly,  or  even 
with  considerable  rapidity,  and  sufficient  attachment  of 
the  principal  fibers  of  the  membrane  be  maintained  to 
hold  the  tooth  securely  while  its  position  is  being  changed. 
Parts  of  the  fibers  are  cut  away  and  some  portions  of  the 
bone  removed,  then  the  fibers  are  reformed  and  built  into 
the  wall  of  the  alveolus  by  a  new  deposit  of  bone  about 
their  ends.  These  changes  are  not  confined  to  young 
animals,  or  young  persons,  but  may  be  found  in  progress 
in  the  old  as  well,  but  are  generally  more  irregular.  I 
have  not  had  the  opportunity  of  examining  a  case  in 
which  the  artificial  movement  of  the  teeth,  as  in  the  cor- 
rection of  irregularities,  has  been  made,  but  from  what  I 
have  seen  I  suppose  that  the  absorption  and  rebuilding 


124  ABSORPTIONS   IN   THE   ALVEOLUS. 

occurs  in  precisely  the  same  way.  However,  in  the  rapid 
movements  that  are  often  made  in  these  cases,  there  must 
be  a  solid  line  of  absorption  along  one  portion  of  the  al- 
veolus (that  pressed  against)  detaching  the  fibers  en 
masse,  while  the  fibers  on  the  other  side  are  lengthened. 
Hence,  the  tendency  of  the  tooth  to  return  to  its  old  posi- 
tion until  time  enough  has  elapsed  for  a  sufficient  refor- 
mation of  its  alveolus  and  the  reattachment  of  its  fibers. 

In  adults  evidences  of  changes  in  the  alveolar  wall 
may  be  found  about  almost  any  tooth  (so  far  as  my  ob- 
servation has  extended)  that  has  changed  position  from 
the  loss  of  neighboring  teeth.  In  fig.  64  I  present  an 
illustration  from  the  alveolar  wall  at  the  posterior  surface 
of  a  bicuspid  that  had  moved  backward  slightly  from  the 
loss  of  the  crown  of  the  second  bicuspid.  The  bone,  6,  6, 
seems  to  have  been  built  in  to  supply  an  area  of  absorp- 
tion that  was  considerably  more  than  the  needs  of  the 
actual  movement  of  the  root.  That  this  has  been  an  ab- 
sorption is  clearly  shown  by  the  Haversian  systems  of  the 
bone  being  cut  into  and  portions  of  their  rings  removed, 
as  is  shown  all  along  the  line.  At  e,  a  recent  absorption 
has  occurred,  and  from  the  presence  of  three  osteoclasts 
(*)  it  is  seen  to  have  been  in  actual  progress  at  the  time 
of  the  death  of  the  individual.  Such  absorptions  as  this 
latter  are  not  infrequent  in  the  alveolar  walls.  They 
seem  to  occur  without  any  cause  that  I  have  been  able  to 
trace,  though  it  is  probable  that  they  are  stimulated  by 
some  slight  movement  of  the  tooth,  and  have  proceeded 
beyond  the  needs,  and  are  again  refilled  by  the  deposit  of 
bone. 

In  a  large  number  of  examinations  very  many  spaces 
will  be  found  at  which  there  seems  to  be  no  attachment 
of  the  membrane  to  the  bone,  and  yet  the  appearance  of 
residual  fibers  within  the  bone  shows  plainly  that  the 
fibers  have  previously  been  attached  here.  In  these'  cases 
there  is  sometimes  evidence  of  absorption  of  the  surface 


ABSORPTIONS   IN   THE   ALVEOLUS.  125 

of  the  bone,  sometimes  not,  but  it  seems  most  probable 
that  the  fibers  have  been  removed  by  this  process, 
though  this  may  occur  from  some  process  not  yet  noted. 
Precisely  the  same  thing  occurs  along  the  surface  of  the 
cementum,  sometimes  evidently  from  absorption  of  the 
surface  of  the  cementum,  but  sometimes  such  absorptions 
cannot  be  demonstrated.  Absorptions  of  the  cementum 
are  not  so  frequent  as  those  of  the  alveolus. 

In  fig.  65  I  present  an  illustration  exhibiting  the  evi- 
dences of  absorption  of  portions  of  the  root  of  a  lower 
molar.  In  absorptions  of  the  cementum  in  cases  in  which 
it  has  not  been  so  great  as  to  obliterate  the  lamellae  we 
may  do  much  in  the  way  of  fixing  the  time  of  the  occur- 
rence relatively  to  the  laying  down  of  the  individual 
lamellae,  in  the  same  way  that  we  can  fix  the  relative 
time  of  the  formation  of  hypertrophies  of  the  cementum 
described  in  chapter  XIII.  These  absorptions  are  found 
to  have  broken  through  certain  of  the  lamellse  and  ex- 
tended, perhaps  as  those  shown  at  d,  fig.  65,  considerably 
into  the  dentine.  .They  are  afterward  repaired  by  the 
deposit  of  cementum,  and  the  lamellse  of  cementum  sub- 
sequently laid  down  are  seen  to  pass  over  them  without 
material  disturbance.  In  all  such  cases  we  know  that  the 
absorption  has  occurred  very  early  in  the  history  of  the 
tooth,  otherwise  it  would  have  broken  through  the  lamellae 
deposited  later.  In  the  study  of  the  subject  we  shall  find 
these  beginning  with  any  of  the  lamellse  of  the  cementum, 
from  first  to  last,  as  the  absorption  has  occurred  early  or 
late  in  life.  In  fig.  66  a  pit-like  absorption  has  extended 
from  the  surface  through  all  of  the  lamellse  of  the  cemen- 
tum except  the  first,  almost  reaching  the  dentine.  This 
was  from  an  old  man,  and  was  evidently  very  recent,  for 
the  process  of  repair  seems  just  begun  and  is  apparently 
in  active  progress. 

The  greater  number  of  absorptions  that  I  have  studied 
seem  to  have  begun  in  the  second  or  third  distinct  lamellae, 


126  ABSORPTIONS  IN   THE   ALVEOLUS. 

and  have  probably  been  contemporaneous  with  the  first 
use  of  the  tooth,  at  a  time  when  it  is  forced  a  little  to 
this  side  or  that  for  the  filling  of  its  cusps  into  the  sulci 
of  the  opposing  tooth.  At  e,  in  fig.  65,  an  absorption  of 
much  greater  extent  is  shown.  This  seems  to  have  cut 
away  the  entire  apex  of  the  root.  Absorptions  as  exten- 
sive as  this  are  much  more  rare  than  those  previously 
noted,  but  close  observation  of  teeth  extracted  will  within 
a  few  years  reveal  a  goodly  number  of  such.  They  are 
found  in  teeth  that  seem  to  have  rather  short,  thick 
roots,  often  with  an  irregular  surface.  Sometimes  these 
will  be  found  upon  microscopic  examination  to  be  recent 
absorptions  in  which  the  dentine  is  exposed.  Again, 
they  will  be  found  covered  with  a  fresh  deposit  of  cemen- 
tum.  In  the  greater  number  of  cases  a  close  study  of  the 
lamellae  of  the  cementum  will  give  a  clue  to  the  time  of 
the  absorption.  For  this  purpose  it  is  necessary  that  the 
section  be  carried  directly  at  right  angles  with  the 
lamellae,  for  otherwise  they  will  not  appear  distinctly. 
It  is  therefore  practically  impossible  to  study  every  part 
of  a  root.  But  generally  enough  sections  can  be  had 
from  lengthwise  cuts  to  give  a  good  idea  of  it. 

In  fig.  65  a  study  of  the  lamellae  of  the  cementum 
shows  that  the  absorption  which  shortened  the  root  at  e 
occurred  early  in  the  history  of  the  tooth,  and  that  it  was 
promptly  recovered  with  cementum.  The  incremental 
lines  do  not  appear  very  plainly  in  this  part,  hut  they 
lead  into  it  in  such  a  way  as  to  leave  no  doubt.  In  other 
cases  that  I  have  examined,  that  were  outwardly  similar, 
and  which  might  be  illustrated,  the  absorptions  have 
occurred  late  in  the  tooth's  history,  the  absorption  having 
broken  through  the  greater  number  of  the  lamellae,  or 
have  been  recent,  as  the  absorption  at/,  fig.  65,  in  which 
there  seems  to  have  been  no  effort  at  repair. 

From  the  examinations  that  I  have  made  I  am  led  to 
the  opinion  that  absorptions  of  this  nature  in  the  roots  of 


ABSORPTIONS    IN   THE    ALVEOLUS.  127 

the  permanent  teeth  do  not  remain  long  without  the 
occurrence  of  the  reparative  effort,  if  -the  tissues  are  in  a 
condition  for  this  effort  to  be  made.  It  may  also  be  stated 
that,  if  the  tissues  are  in  a  condition  to  produce  absorp- 
tion, they  will  also  be  in  a  condition  to  make  the  repair, 
provided  no  impairment  has  occurred  in  the  meantime. 
Fig,  66,  from  a  section  cut  from  the  immediate  apex  of 
the  root  of  a  cuspid,  shows  something  of  the  extent  and 
completeness  of  these  repairs. 

A  class  of  absorptions  precisely  similar  to  that  illus- 
trated in  fig.  66,  is  of  rather  frequent  occurrence  near  the 
gingival  margin  of  the  cementum.  I  have  called  atten- 
tion to  these  heretofore,  and  at  various  times,  in  the  con- 
sideration of  caries  of  the  teeth,  and  especially  in  the 
appendix  to  "  Formation  of  Poisons  by  Micro-organisms," 
page  168,  and  in  the  "American  System  of  Dentistry," 
vol.  I,  p.  777.  These  absorptions  are  very  generally  of 
the  form  of  that  illustrated  in  fig.  66,  and  when  they 
occur  very  close  to  the  attachment  of  the  membrane  at 
the  gingival  border,  are  liable  to  become  uncovered  by 
the  shrinkage  of  the  soft  tissues  and  afford  lodgement  for 
micro-organisms,  and  thus  are  a  predisposing  cause  of 
caries.  I  have  often  noted  quite  broad  absorption  areas 
at  this  point  which  seem  to  remove  that  portion  of  the 
cementum  which  laps  upon  the  enamel,  producing  a 
marked  groove.  This  is  occasionally  more  extended, 
cutting  considerably  into  the  dentine,  and  in  case  it 
becomes  exposed,  gives  the  opportunity  for  the  girdling 
of  the  tooth,  in  whole  or  in  part,  by  caries  becoming 
implanted  in  it.  I  have  seen  several  instances  in  which 
the  tooth  was  almost  severed  from  its  root  by  these  cer- 
vical absorptions.  One  lower  molar  in  my  possession  had 
an  absorption  beginning  upon  the  mesial  surface,  that 
invaded  the  pulp  cavity.  In  another  case  now  under  ob- 
servation such  an  absorption  so  weakened  a  lower  incisor 
that  the  crown  broke  away.  A  number  of  similar  cases 


128  ABSORPTIONS   IN   THE   ALVEOLUS. 

might  be  mentioned.  These  might  be  mistaken  for  caries, 
if  the  condition  of  the  surface,  and  the  tissues  filling  the 
space,  were  not  carefully  observed.  But  the  condition  is 
so  different  in  the  two  cases  that  a  mistake  should  not 
occur.  Of  course,  after  caries  has  once  invaded  the  part, 
there  is  no  means  of  knowing  whether  an  absorption  began 
the  breach  or  not. 

From  the  studies  previously  cited  it  seems  that  the 
detachment  and  reattachment  of  the  peridental  mem- 
brane in  parts  here  and  there  is  continually  occurring. 
Not  only  is  this  the  case  where  there  has  been  appreci- 
able absorption  of  the  cementum,  as  in  the  cases  illus- 
trated, but  a  study  of  the  fibers  included  in  the  cemen- 
tum shows  unmistakably  that  they  have  been  broken  at 
many  of  the  incremental  lines  when  absorption  cannot  be 
demonstrated.  In  these  cases  the  constant  reappearance 
of  the  fibers  in  the  lamellae  subsequently  deposited  shows 
that  the  plan  of  the  reattachment  is  by  new  deposits  of 
cementum  upon  the  old.  In  this  new  deposit  the  ends  of 
the  fibers  are  imbedded,  making  a  firm  hold.  This  occurs 
equally  well  if  the  new  deposit  be  upon  the  denuded 
dentine,  as  when  it  is  upon  the  cementum.  This  being 
the  constant  method  in  this  class  of  cases,  I  must  now 
suppose  that  in  the  various  modes  of  planting  natural 
teeth,  the  manner  of  attachment  to  the  root  is  the  same. 
That  is  to  say,  the  attachment  of  the  tooth  depends  upon 
the  production  of  a  lamella  of  cementum  covering  the 
root.  This  lamella  of  cementum  is  laid  down  upon  the 
root  by  the  tissues  in  contact  with  it.  It  does  not  seem 
to  depend  upon  the  vitality  of  the  cementum  upon  which 
it  is  deposited.  It  does  not  grow  from  the  cementum, 
but  from  the  soft  tissues — from  the  cemento-blasts.  If 
this  lamella  of  cementum  is  once  perfectly  formed,  there 
would  appear  to  be  no  reason  why  it  should  not  endure, 
but  the  apparent  difficulty  is  to  obtain  that  perfect  la- 
mella of  cementum  ;  and  the  absorptions  continue  little 


ABSORPTIONS    IN    THE   ALVEOLUS.  129 

by  little,  proceeding  from  the  many  imperfect  points,  un- 
til the  root  is  destroyed.  This  appears  from  studies  now 
made.  Future  investigations  may  reveal  new  factors  not 
yet  noted. 

I  have  now  finished  the  task  I  set  myself  to  perform 
— a  practical  histological  study  of  the  periosteum  and 
peridental  membrane.  The  task  has  been  difficult  in 
many  respects,  and  has  required  an  amount  of  labor  much 
greater  than  was  expected  in  the  beginning.  Although  I 
had  much  available  material,  I  have  thought  it  best  to 
make  new  preparations  of  all  the  tissues.  These  have 
all  been  gathered,  and  the  work  done  since  the  first  of 
October  of  last  year.  As  the  work  progressed  it  was 
found  that  a  number  of  series  of  sections  were  required 
for  study  in  special  directions,  which  greatly  increased 
the  labor.  All  of  the  illustrations  are  made  from  freshly 
prepared  material.  The  work  is  now  before  the  profes- 
sion, and  by  the  profession  its  value  must  be  judged. 
Many  phases  of  the  subject  are  new.  Very  few  studies 
of  these  tissues  had  been  made  by  previous  observers. 
Therefore,  extended  references  do  not  seem  to  be  called 
for.  Indeed,  the  literature  does  not  furnish  them.  Hy- 
pertrophies and  absorptions  of  the  cementum  have  been 
studied  by  John  Tomes,  Chas.  Tomes,  C.  Wedl,  Salter 
and  others,  and  among  these  some  very  brief  examinations 
of  the  peridental  membrane  appear.  Among  the  works 
on  general  histology  there  is  some  brief  mention  of  the 
characters  of  the  periosteum  and  peridental  membrane, 
and  several  have  mentioned  the  presence  of  residual 
fibers  (fibers  of  Sharpey)  in  the  cementum.  Such  notices 
have,  however,  been  too  sparse  to  give  much  information 
on  the  subject.  However,  after  studying  these  papers, 
the  reader  will  do  well  to  review  any  and  all  of  these  that 
may  be  within  his  reach. 


INDEX. 


A. 

Absorption  at  the  gingival  margin 127 

a  predisposing  cause  of  caries 127 

bone  corpuscles  passive  in  areas  of 121 

cells  development  of 68 

detachment  of  the  fibers  of  the  peridential  membrane  by  128 

irregularities .  of 121 

of  bone 48,  44 

of  the  roots  of  the  temporary  teeth 118 

of  the  roots  of  the  temporary  teeth  prevented  by  disease.  118 
of  the  roots  of  the  temporary  teeth  not  prevented   by 

death  of  the  tooth's  pulp 120 

of  the  alveolar  wall 122 

passive  condition  of  tissues  acted  upon  by -  120 

relation  of  irritation  to 120 

repair  of  breaches  made  by 125,  127 

roots  of  teeth  shortened  by 126 

the  process  of 119 

Absorptions  occurring  within  the  alveolus 118 

Acids  effects  of,  on  tissues 4 

"       on  selective  stainings 4 

Apical  space 73 

fibers  of  the • 77 

Alveolar  wall,  absorptions  of  the 122 

evidences  of  changes  in  the,  in  adults 124 

Haversian  canals  of  the 97 

manner  of  the  growth  of  the 98 

movements  of  the  teeth  during  the  growth  of  the. ..  98 
relations  of  the  growth  of  the,  to  the  elongation  of 

the  face 100 

B. 

Basis  substance _ 8 

Blood  vessels  of  the  periosteum , 35 

of  the  peridental  membrane 85 

Bone,  beginnings  of  the  deposit  of  sub-periosteal 64 

conversion  of  articular  cartilage  into 57 

diaphy sal  formation  of 57,  62 

epiphysal  formation  of 57,  58 

first  deposit  of,  in  cartilage 68 

formation  of 45 

formation,  osteoblasts  the  agents  of 70 

formed  under  the  attached  periosteum 42 

growth  of  the  shaft  of ,  in  length 65 

S'owth  of,  under  tendonous  attachmen  ts 55 

aversian  systems  of 46 

131 


132  INDEX. 

Bone,  intra-membrmous  formation  of 16,  52 

intra-cartilaginous    formation  of - 57 

lammellae  of 46 

length  of,  not  increased  by  interstitial  growth ..  65 

modes  of  the  formation  of T... 16,  45 

penetrating  fibers  of 46 

removal  of  the  penetrating  fibers  of 47 

subperiosteal  formation  of 45,  57 

two  distinct  modes  of  replacement  of  cartilage  with. 57 

Bone  corpuscles  ". 41 

processes  of 42 

position  of  the,  in  bone _ 43 

'          relation  of  the,  to  the  surface  of  the  forming  bone..  46 

Boll 11 

C. 

Calcospherites  in  the  peridental  membrane 94 

Cartilage,  absorption  of       59,64,  68 

calcification  of  the  matrix  of 66 

cells 63 

changes  in  epiphysal,  preparatory  to  the  formation  of  bone  58 
changes  in  dhphysal,   preparatory  to  the  formation  of 

bone 62 

changes  in  the  cells  of 63 

condition  of  nuclei  of,  cells  before  absorption 65 

continuous  growth  of  articular 62 

destiny  of  the,  cells     60,  61 

division  of  the  cells  of 63 

deposit  of  bone  upon 59 

infiltration  of ,  with  lime  salts  ... 59 

manner  of  the  absorption  of  diaphysal 66 

opening  of  the  capsules  of,  cells  by  absorption _.  66 

passive  condition  of  cells  of,  before  absorption 65 

pierced  by   capillaries 64 

pigmented ...  66 

special  reaction  of,  to  stains 66 

Caustic  potass,  used  in  demonstrating  elastic  fibers 34 

Cells,  development  of,  in  ground  substance - 8 

cartilage 63 

cartilage,  disintegration  of  neuclei  of 66 

degeneration  of  cartilage 65 

development  of  absorption 69 

marrow 64 

marrow,  in  regions  of  absorption  of  cartilage 65 

Cellular  elements  of  membranes 13 

of  the  periosteum 37 

of  the  peridental  membrane 72 

Cement  corpuscles 104 

processes  of  the 104 

Cementoblasts 102 

different  from  osteoblasts 102 

processes  of  the 103 

relations  of  the,  to  the  fibers  of  the  peridental  mem- 
brane  103 

relations  of  the,  to  growth  of  cementum... 104 

sections  for  displaying  the  form  of  the.. 103 


INDEX.  133 

Cementum 102,  104 

continuous  growth  of  the - 107,  111 

deposit  of,  in  lamellae ^ 105 

development  of  the  lamellae  of  the . .'.  112 

fibers  of  the 108 

fibers  of  the,  demonstrated  in  cross  section 109 

fusion  of,  with  cementum. 117 

hypertrophies  confined  to  one  or  a  few  lamellae  of  the...  113 

hypertrophies  of  the - Ill 

inclusion  of  blood  vessels  in  the 106 

incremental  lines  of  the _. 106 

irregularities  in  the  growth  of  the Ill 

knob-like  thickenings  of  the 115 

modes  of  study  of  irregularities  in  the  growth  of  the 112 

no  Haversian  systems  in  the 106 

non-union  of ,   with  bone 116 

theory  as  to  the  cause  of  irregularities  in  the  growth  of 

the 113 

Chemical  relations  of  the  tissues,  with  regard  to  stainings 4 

Chondroclasts 61 

development  of 69 

Cohesion _ _ 1 

Connective  tissue,  primary _.       8 

Connective  tissues,  develo'pmental  relations  of  the 15 

' '        appropriateness  of  the  name 16 

D. 

Dentine,  physiological  connections  of  the 105 

Development  of  connective  tissue 7 

"        of  elastic  fibers 11 

Ducts  of  the  lymphatics  of  the  peridental  membrane 91 

E. 

Elastic  fibers 11 

development  of . .  11 

distribution  of _ 12 

manner  of  demonstrating  the 33 

of  the  periosteum 33 

Elastin  connecting  the  epithelia . 12 

"      granules  of 12 

"      homogeneous  membranes  of _ 12 

Elongation  of  the  face  during  the  growth  of  the  alveolar  walls 99 

F. 

Face,  movements  of  the  teeth  during  elongation  of  the 99 

Fatty  tissue 14 

Fibers,  arrangement  of,  in  the  peridental  membrane 75 

bundles  of 10 

coarse,  seldom  round 10 

coarse,  in  cross  section - 10 

detachment  of  the,  of  the  peridental  membrane 123 

development  of 9 

development  of  yellow  elastic ..  11 


134  INDEX. 

Fibers,  inter-locking  of 10 

"      manner  of  branching 10 

"      meshes  formed  of 10 

"      of  the  cementum 108 

' '      of  the  cementum  demonstrated  in  cross  section 109 

' '      principal,  of  the  peridental  membrane 74 

"      osteogenetic 50 

14      principal,  of  the  peridental  membrane  included  in  the  ce- 
mentum  109 

4<      reticular 11 

"      relations  of ,  to  forming  bone 50 

"      varieties  of 8 

"      white  inelastic -. 8 

"      yellow  elastic 8,  11 

Fibrilation... 9 

Fibroblasts 9 

Fibrous  elements  derived  from  cells 8 

Fibrous  membranes,  functions  of  the 14 

histology  of  the v. 6 

"            local  characteristics  of  the 14 

names  of  the 14 

"           relations  of  the,  to  cartilage  and  bone 15 

Fibrous  tissue,  substitutions  of 16 

Formation  of  secondary  Haversian  systems  in  bone  .  - 47,  48 

Fusion  of  cementum  with  cementum 123 

G. 

Gelatinous  substance 8 

"         tissue 8 

Giant  cells 43 

Gingivus,  the 76 

Ground  substance 8 

Growth  of  bone  on  inner  surface  of  alveolar  wall 96 

under  tendonous  attachments _ 55 

under  articular  cartilage 57 

Gum,  border  of  the,  described 76 

H. 

Hard  formations  within  the  peridental  membrane 94 

Haversian  canals  of  the  alveolar  wall 97 

"      formation  of,  by  the  removal  of  bone 47 

"      formation  of,  in  tendonous  attachments. 55 

"      relations  of  the  penetrating  fibers  of  bone  to  the  ..  47 

Haversian  systems  of  bone 46 

"                      secondary 47 

Histology  of  the  fibrous  membranes 6 

Howship,  lacunae  of 43 

I. 

Illustrations,  how  made 20 

Impregnation  of  tissues  for  cutting  sections 18 

for  cutting  sections  in  bay  berry  tallow. 18 

'•             for  cutting  sections  in  celloidin 18 

' '             for  cutting  sections  in  gum  arabic 18 

"              "             for  cutting  sections  in  paraffin 18 


INDEX. 


135 


Incremental  lines  of  the  cementum 106 

Intra-membranous  formation  of  bone  ., 52 

Intra-cartalaginous  formation  of  bone 57 

of  bone,  diaphysal 62 

of  bone,  epiphysal 58 

Irregularities  in  the  growth  of  the  cementum .' Ill 

K. 

Krause  11 

Klein _.. ' 91 

L. 

Lacunae  of  Howship 43 

Lamellae  of  the  cementum 105 

relation  of  numbers  of  the,  to  the  age  of 

the  individual 105 

represent  periods  of  activity  of  growth  . .  105 

Ligamentum  nuchea... 12 

Ligamentum  subflava 12 

Localization  of  the  sense  of  touch  for  the  teeth,  experiments 88 

Lymphatics  of  the  peridental  membrane .72,  90 

double  stainings  of  the  ....  91 

ducts  of  the 91 

in  different  animals  _ 92 

individual  cells  of  the  .....  91 

limiting  membrane  of  the  .  91 
probable  connection  of  the, 

with  destructive  percementitis 92 

Lymph  nodes  of  the  peridental  membrane 91 

Lymph  cells  of  the  peridental  membrane 91 

M. 

Matrix 8 

Marrow  cells  - ..  64 

Membrane,  limiting,  of  the  lymphatics  of  the  peridental  membrane  91 

Membranes,  cellular  elements  of. 13 

"          subordinate  to  functionary  tissues 16 

"          subordinate  to  relations  of  the 16 

Methods  of  the  preparation  of  tissues 17 

Movements  of  the  permanent  teeth  in  their  sockets  during  elonga- 
tion of  the  face 99 

Mueller's  fluid 17 

Myoplaxies 43 

Myxomatuous  tissues.. _  8 

N. 

Nerves  of  the  periosteum 36 

"  "  "  peridental  membrane 87 

"  terminations  in  peridental  membrane 88 

Notch-pereosteal 57 


136 


INDEX. 


O. 

Organ  of  touch  of  the  teeth -- 88 

Osteoblasts 38,  102 

description  of  the - 38 

development  of,  on  the  surface  of  cartilage 63 

'         forms  of  the,  in  old  persons 39 

'         functions  of  the --   40 

in  the  Haversian  canals ...  39 

'         opinion  as  to  where  the,  belong 38 

place  of  the 38,  39 

suppositions  as  to  the  way  bone  is  built  by  the  40 

'         the  only  agents  of  bone  formation 70 

'         and  the  alveolar  walls - 96 

Osteoclasts,  ameboid  movements  of  the 44 

'          at  the  ends  of  the  long  bones 26 

description  of  the 43 

functions  of  the 44 

'          lacunae  of  Howship  formed  by  the 43 

Osteogenetic  fibers '. ..- 50 

Osteogenetic  substance. 50 

P. 

Pain,  sense  of,  in  the  peridental  membrane 88 

Penetrating  fibers  of  bone 46 

"       "      "    calcification  of  the... —  51 

"              "       "      "    removal  of  the 47,  52 

Perichondrium.. 63 

"            changed  to  periosteum. 64 

Peridental  membrane,  attention  called  to  the 3 

and  periosteum,  kinship  of  the 4 

and  periosteum,  difficulties  in  the  study  of  the  7 

arrangement  of  the  fibers  of  the 75 

blood  supply  of  the 85 

cellular  elements  of  the 72 

changed  appearance  of  the  tissues  of  the,  in 

old  age 82 

components  of  the - 72 

diminished  thickness  of  the,  in  old  age 79 

divisions  of  the 72 

direction  of  the  fibers  of  the 73 

direction  of  the  fibers  of  the  body  of  the 77 

detachment  and  re-attachment  of  the 128 

facicular  arrangement  of  the  fibers  of  the.  .80,  82 

fibers  of  the.- 74 

fibers  of  the,  inelastic 79 

fibers  of  the  lower  border  of  the 76 

fibers  of  the  apical  space 77 

form  of  the 72 

form  of  the  principal  fibers  of  the 79 

functions  of  the 71 

indifferent  tissue  of  the 84 

inter-fibrous  elements  of  the 84 

lymphatics  of  the 12,  90 

nerve  terminations  in  the  . ,  88 


INDEX.  137 

Peridental  membrane,  office  of  the 71 

physical  functions  of  the 71,  79 

physical  functions  of  the  fibers  of  the 79 

pigment  granules  in  the 95 

principal  fibers  of  the 71,  74 

relation  of  the  cementoblasts  to  the  fibers  of  the  103 

sensory  functions  of  the 71,  87 

sensory  functions  of  the,  not  destroyed  by  in- 
jury to  any  one  portion 89 

the,  the  organ  of  touch  for  the  tooth 88 

thickness  of  the 73 

variations  in  the  arrangement  of  the  fibers  of 

the 78 

"          variations  in  the  appearance  of  the  fibers  of 

the 78,  80 

"          vascular  region  of  the 81 

Periosteal  notch . 57 

Periosteum,  blood  vessels  of  the 35 

cells  of  the,  not  showing  specific  character . . . .  37 

cellular  elements  of  the.. 37 

embryonal  cell  among  the  fibers  of  the 38 

gross  examination  of  the 22 

histological  character  of  the _ 24 

nerves  of  the 36 

previous  studies  of  the. ..  .  7 

where  the,  is  adherent  to  the  bone 23 

where  the,  is  separable  from  the  bone 23 

Periosteum,  internal  layer,  appearance  with  selective  stains 30 

' '     appearance  with  diffusive  stains. . . 30 

"      arrangement  of  the  fibers  of  the,  on  the 

long  bones 30 

"      arrangement  of  the  fibers  of  the,  on  the 

short  bones 30 

"      attached  forms  of  the,  described 31 

"      attached  and  non  attached  forms  of  the.  29 

' '      character  of  the  fibers  of  the 29 

"      de  novo  development  of  the 64 

"      destitute  of  elastic  fibers.. 35 

"      in  attached  regions  of  the  long  bones. ..  31 

"      in  non-attached  regions  of  the  long  bones  31 

•'      non-attached  form  of  the,  described 29 

"      plan  of  the  fibers  of  attached,  form  of  the  32 

"          "      relation  of  the  fibers  of  the,  to  the  bone.  32 

external  layer  of  the 24 

"         "      arrrangement  of    the,   for  sliding 

movements  of  tissues  upon  it.25,  29 
"        "      arrangement  of  the,  on  the  shafts 

of  the  long  bones 26 

"          "        "      arrangement  of  the,  at  the  ends  of 

the  long  bones... 26 

"         "      arrangement  of  the,  on  the  bones 

'of  the  face 27 

"        "      attachment  of  muscles  to  the 29 

"          "        "      attachment  of  facese  to  the 29 

"        "      character  of  the  coarse  fibers  of  the  25 
"        "      complex  arrangement  of  the  fibers 

of  the 25 

1 8. 


138  INDEX. 

Periosteum,  external  layer  of  the  lamellae  of  the 25 

"                  "          "        "      ribbon-like  layers  of  the 25 

"                  "          • '        "      simpler  form  of  the . .  26 

"                  "          "         "      sometimes  absent 28 

"  "          "        "      sometimes    blended     with    other 

structures . .  28 

"  "          "        •'      sometimes  united  to  other  tissues 

by  elastic  fibers - 

"                  "          "         "      where  thick  and  where  thin 24 

Phleboliths 94 

Physiological  errors .. ..37,  118 

Pigmentation,  plan  of. 19 

Pigment  granules  in  the  peridental  membrane 95 

Preliminary . . . .  1 

Preparation  of  tissues,  acids  in  the IT 

methods  of  the -... 17 

Mullers  fluid  in  the 17 

time  as  an  element  in  the 17,  19 

injurious  effects  of  acids  in  the 17 

use  of  alcohol  in  the 18 

Processes  of  the  bone  corpuscles 42 

"        "       cement  corpuscles 104 

R. 

Replantation  of  teeth . 3 

Residual  fibers  of  bone 49 

"        "        functions  of  the 49 

"          "     of  the  alveolar  wall 97 

Reticular  fibers 10 

Riggs,  Dr.,  of  Hartford 3 

Roots  of  teeth  shortened  by  absorption 126 

S. 

Salter. 93,  129 

Salivary  corpuscles « 94 

Sensory  function  of  the  peridental  membrane 87 

Serres - 93 

Sharpey's  fibers. 49 

Shrinkage  of  tissues 4 

Space,  the  apical 73 

Staining  tissues,  plans  of - 19 

Strieker 1 

Subperiosteal  formation  of  bone 45 

T. 

Technique,  advances  in.. 2 

Tendinous  attachments  growth  of  bone  under 55 

Tendo-achillis,  growth  of  bone  under  attachment  of . 55 

Tissue  elements  and  their  distribution. 6 

Tomes,  John  ... 129 

Tomes,  Charles 129 

Transplantation  of  teeth 3 

Two  modes  of  replacement  of  cartilage  by  bone 57 

W. 

Wedl 129 

Y. 

Yellow  elastic  tissue . .  11 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 

Los  Angeles 

Tl-i-  »• *-  * 

University  of  <*Momla 
SOUTHERN  REGIONAL  UBRARY 

405 


from  which  It  was 

• 

,^o't  \  i^r-ry 


Form  L9-116m 


A     000414479     6 


